core tests

core/shared/application/AsyncUseCase.test.ts

@@ -0,0 +1,412 @@
+import { describe, it, expect } from 'vitest';
+import { AsyncUseCase } from './AsyncUseCase';
+import { Result } from '../domain/Result';
+import { ApplicationErrorCode } from '../errors/ApplicationErrorCode';
+
+describe('AsyncUseCase', () => {
+  describe('AsyncUseCase interface', () => {
+    it('should have execute method returning Promise<Result>', async () => {
+      // Concrete implementation for testing
+      class TestAsyncUseCase implements AsyncUseCase<{ id: string }, { data: string }, 'NOT_FOUND'> {
+        async execute(input: { id: string }): Promise<Result<{ data: string }, ApplicationErrorCode<'NOT_FOUND'>>> {
+          if (input.id === 'not-found') {
+            return Result.err({ code: 'NOT_FOUND' });
+          }
+          return Result.ok({ data: `Data for ${input.id}` });
+        }
+      }
+
+      const useCase = new TestAsyncUseCase();
+
+      const successResult = await useCase.execute({ id: 'test-123' });
+      expect(successResult.isOk()).toBe(true);
+      expect(successResult.unwrap()).toEqual({ data: 'Data for test-123' });
+
+      const errorResult = await useCase.execute({ id: 'not-found' });
+      expect(errorResult.isErr()).toBe(true);
+      expect(errorResult.unwrapErr()).toEqual({ code: 'NOT_FOUND' });
+    });
+
+    it('should support different input types', async () => {
+      interface GetUserInput {
+        userId: string;
+        includeProfile?: boolean;
+      }
+
+      interface UserDTO {
+        id: string;
+        name: string;
+        email: string;
+        profile?: {
+          avatar: string;
+          bio: string;
+        };
+      }
+
+      type GetUserErrorCode = 'USER_NOT_FOUND' | 'PERMISSION_DENIED';
+
+      class GetUserUseCase implements AsyncUseCase<GetUserInput, UserDTO, GetUserErrorCode> {
+        async execute(input: GetUserInput): Promise<Result<UserDTO, ApplicationErrorCode<GetUserErrorCode>>> {
+          if (input.userId === 'not-found') {
+            return Result.err({ code: 'USER_NOT_FOUND' });
+          }
+
+          if (input.userId === 'no-permission') {
+            return Result.err({ code: 'PERMISSION_DENIED' });
+          }
+
+          const user: UserDTO = {
+            id: input.userId,
+            name: 'John Doe',
+            email: 'john@example.com'
+          };
+
+          if (input.includeProfile) {
+            user.profile = {
+              avatar: 'avatar.jpg',
+              bio: 'Software developer'
+            };
+          }
+
+          return Result.ok(user);
+        }
+      }
+
+      const useCase = new GetUserUseCase();
+
+      // Success case with profile
+      const successWithProfile = await useCase.execute({
+        userId: 'user-123',
+        includeProfile: true
+      });
+
+      expect(successWithProfile.isOk()).toBe(true);
+      const userWithProfile = successWithProfile.unwrap();
+      expect(userWithProfile.id).toBe('user-123');
+      expect(userWithProfile.profile).toBeDefined();
+      expect(userWithProfile.profile?.avatar).toBe('avatar.jpg');
+
+      // Success case without profile
+      const successWithoutProfile = await useCase.execute({
+        userId: 'user-456',
+        includeProfile: false
+      });
+
+      expect(successWithoutProfile.isOk()).toBe(true);
+      const userWithoutProfile = successWithoutProfile.unwrap();
+      expect(userWithoutProfile.id).toBe('user-456');
+      expect(userWithoutProfile.profile).toBeUndefined();
+
+      // Error cases
+      const notFoundResult = await useCase.execute({ userId: 'not-found' });
+      expect(notFoundResult.isErr()).toBe(true);
+      expect(notFoundResult.unwrapErr()).toEqual({ code: 'USER_NOT_FOUND' });
+
+      const permissionResult = await useCase.execute({ userId: 'no-permission' });
+      expect(permissionResult.isErr()).toBe(true);
+      expect(permissionResult.unwrapErr()).toEqual({ code: 'PERMISSION_DENIED' });
+    });
+
+    it('should support complex query patterns', async () => {
+      interface SearchOrdersInput {
+        customerId?: string;
+        status?: 'pending' | 'completed' | 'cancelled';
+        dateRange?: { start: Date; end: Date };
+        page?: number;
+        limit?: number;
+      }
+
+      interface OrderDTO {
+        id: string;
+        customerId: string;
+        status: string;
+        total: number;
+        items: Array<{ productId: string; quantity: number; price: number }>;
+        createdAt: Date;
+      }
+
+      interface OrdersResult {
+        orders: OrderDTO[];
+        total: number;
+        page: number;
+        totalPages: number;
+        filters: SearchOrdersInput;
+      }
+
+      type SearchOrdersErrorCode = 'INVALID_FILTERS' | 'NO_ORDERS_FOUND';
+
+      class SearchOrdersUseCase implements AsyncUseCase<SearchOrdersInput, OrdersResult, SearchOrdersErrorCode> {
+        async execute(input: SearchOrdersInput): Promise<Result<OrdersResult, ApplicationErrorCode<SearchOrdersErrorCode>>> {
+          // Validate at least one filter
+          if (!input.customerId && !input.status && !input.dateRange) {
+            return Result.err({ code: 'INVALID_FILTERS' });
+          }
+
+          // Simulate database query
+          const allOrders: OrderDTO[] = [
+            {
+              id: 'order-1',
+              customerId: 'cust-1',
+              status: 'completed',
+              total: 150,
+              items: [{ productId: 'prod-1', quantity: 2, price: 75 }],
+              createdAt: new Date('2024-01-01')
+            },
+            {
+              id: 'order-2',
+              customerId: 'cust-1',
+              status: 'pending',
+              total: 200,
+              items: [{ productId: 'prod-2', quantity: 1, price: 200 }],
+              createdAt: new Date('2024-01-02')
+            },
+            {
+              id: 'order-3',
+              customerId: 'cust-2',
+              status: 'completed',
+              total: 300,
+              items: [{ productId: 'prod-3', quantity: 3, price: 100 }],
+              createdAt: new Date('2024-01-03')
+            }
+          ];
+
+          // Apply filters
+          let filteredOrders = allOrders;
+
+          if (input.customerId) {
+            filteredOrders = filteredOrders.filter(o => o.customerId === input.customerId);
+          }
+
+          if (input.status) {
+            filteredOrders = filteredOrders.filter(o => o.status === input.status);
+          }
+
+          if (input.dateRange) {
+            filteredOrders = filteredOrders.filter(o => {
+              const orderDate = o.createdAt.getTime();
+              return orderDate >= input.dateRange!.start.getTime() &&
+                     orderDate <= input.dateRange!.end.getTime();
+            });
+          }
+
+          if (filteredOrders.length === 0) {
+            return Result.err({ code: 'NO_ORDERS_FOUND' });
+          }
+
+          // Apply pagination
+          const page = input.page || 1;
+          const limit = input.limit || 10;
+          const start = (page - 1) * limit;
+          const end = start + limit;
+          const paginatedOrders = filteredOrders.slice(start, end);
+
+          const result: OrdersResult = {
+            orders: paginatedOrders,
+            total: filteredOrders.length,
+            page,
+            totalPages: Math.ceil(filteredOrders.length / limit),
+            filters: input
+          };
+
+          return Result.ok(result);
+        }
+      }
+
+      const useCase = new SearchOrdersUseCase();
+
+      // Success case - filter by customer
+      const customerResult = await useCase.execute({ customerId: 'cust-1' });
+      expect(customerResult.isOk()).toBe(true);
+      const customerOrders = customerResult.unwrap();
+      expect(customerOrders.orders).toHaveLength(2);
+      expect(customerOrders.total).toBe(2);
+
+      // Success case - filter by status
+      const statusResult = await useCase.execute({ status: 'completed' });
+      expect(statusResult.isOk()).toBe(true);
+      const completedOrders = statusResult.unwrap();
+      expect(completedOrders.orders).toHaveLength(2);
+      expect(completedOrders.total).toBe(2);
+
+      // Success case - filter by date range
+      const dateResult = await useCase.execute({
+        dateRange: {
+          start: new Date('2024-01-01'),
+          end: new Date('2024-01-02')
+        }
+      });
+      expect(dateResult.isOk()).toBe(true);
+      const dateOrders = dateResult.unwrap();
+      expect(dateOrders.orders).toHaveLength(2);
+      expect(dateOrders.total).toBe(2);
+
+      // Error case - no filters
+      const noFiltersResult = await useCase.execute({});
+      expect(noFiltersResult.isErr()).toBe(true);
+      expect(noFiltersResult.unwrapErr()).toEqual({ code: 'INVALID_FILTERS' });
+
+      // Error case - no matching orders
+      const noOrdersResult = await useCase.execute({ customerId: 'nonexistent' });
+      expect(noOrdersResult.isErr()).toBe(true);
+      expect(noOrdersResult.unwrapErr()).toEqual({ code: 'NO_ORDERS_FOUND' });
+    });
+
+    it('should support async operations with delays', async () => {
+      interface ProcessBatchInput {
+        items: Array<{ id: string; data: string }>;
+        delayMs?: number;
+      }
+
+      interface ProcessBatchResult {
+        processed: number;
+        failed: number;
+        results: Array<{ id: string; status: 'success' | 'failed'; message?: string }>;
+      }
+
+      type ProcessBatchErrorCode = 'EMPTY_BATCH' | 'PROCESSING_ERROR';
+
+      class ProcessBatchUseCase implements AsyncUseCase<ProcessBatchInput, ProcessBatchResult, ProcessBatchErrorCode> {
+        async execute(input: ProcessBatchInput): Promise<Result<ProcessBatchResult, ApplicationErrorCode<ProcessBatchErrorCode>>> {
+          if (input.items.length === 0) {
+            return Result.err({ code: 'EMPTY_BATCH' });
+          }
+
+          const delay = input.delayMs || 10;
+          const results: Array<{ id: string; status: 'success' | 'failed'; message?: string }> = [];
+          let processed = 0;
+          let failed = 0;
+
+          for (const item of input.items) {
+            // Simulate async processing with delay
+            await new Promise(resolve => setTimeout(resolve, delay));
+
+            // Simulate some failures
+            if (item.id === 'fail-1' || item.id === 'fail-2') {
+              results.push({ id: item.id, status: 'failed', message: 'Processing failed' });
+              failed++;
+            } else {
+              results.push({ id: item.id, status: 'success' });
+              processed++;
+            }
+          }
+
+          return Result.ok({
+            processed,
+            failed,
+            results
+          });
+        }
+      }
+
+      const useCase = new ProcessBatchUseCase();
+
+      // Success case
+      const successResult = await useCase.execute({
+        items: [
+          { id: 'item-1', data: 'data1' },
+          { id: 'item-2', data: 'data2' },
+          { id: 'item-3', data: 'data3' }
+        ],
+        delayMs: 5
+      });
+
+      expect(successResult.isOk()).toBe(true);
+      const batchResult = successResult.unwrap();
+      expect(batchResult.processed).toBe(3);
+      expect(batchResult.failed).toBe(0);
+      expect(batchResult.results).toHaveLength(3);
+
+      // Mixed success/failure case
+      const mixedResult = await useCase.execute({
+        items: [
+          { id: 'item-1', data: 'data1' },
+          { id: 'fail-1', data: 'data2' },
+          { id: 'item-3', data: 'data3' },
+          { id: 'fail-2', data: 'data4' }
+        ],
+        delayMs: 5
+      });
+
+      expect(mixedResult.isOk()).toBe(true);
+      const mixedBatchResult = mixedResult.unwrap();
+      expect(mixedBatchResult.processed).toBe(2);
+      expect(mixedBatchResult.failed).toBe(2);
+      expect(mixedBatchResult.results).toHaveLength(4);
+
+      // Error case - empty batch
+      const emptyResult = await useCase.execute({ items: [] });
+      expect(emptyResult.isErr()).toBe(true);
+      expect(emptyResult.unwrapErr()).toEqual({ code: 'EMPTY_BATCH' });
+    });
+
+    it('should support streaming-like operations', async () => {
+      interface StreamInput {
+        source: string;
+        chunkSize?: number;
+      }
+
+      interface StreamResult {
+        chunks: string[];
+        totalSize: number;
+        source: string;
+      }
+
+      type StreamErrorCode = 'SOURCE_NOT_FOUND' | 'STREAM_ERROR';
+
+      class StreamUseCase implements AsyncUseCase<StreamInput, StreamResult, StreamErrorCode> {
+        async execute(input: StreamInput): Promise<Result<StreamResult, ApplicationErrorCode<StreamErrorCode>>> {
+          if (input.source === 'not-found') {
+            return Result.err({ code: 'SOURCE_NOT_FOUND' });
+          }
+
+          if (input.source === 'error') {
+            return Result.err({ code: 'STREAM_ERROR' });
+          }
+
+          const chunkSize = input.chunkSize || 10;
+          const data = 'This is a test data stream that will be split into chunks';
+          const chunks: string[] = [];
+
+          for (let i = 0; i < data.length; i += chunkSize) {
+            // Simulate async chunk reading
+            await new Promise(resolve => setTimeout(resolve, 1));
+            chunks.push(data.slice(i, i + chunkSize));
+          }
+
+          return Result.ok({
+            chunks,
+            totalSize: data.length,
+            source: input.source
+          });
+        }
+      }
+
+      const useCase = new StreamUseCase();
+
+      // Success case with default chunk size
+      const defaultResult = await useCase.execute({ source: 'test-source' });
+      expect(defaultResult.isOk()).toBe(true);
+      const defaultStream = defaultResult.unwrap();
+      expect(defaultStream.chunks).toHaveLength(5);
+      expect(defaultStream.totalSize).toBe(48);
+      expect(defaultStream.source).toBe('test-source');
+
+      // Success case with custom chunk size
+      const customResult = await useCase.execute({ source: 'test-source', chunkSize: 15 });
+      expect(customResult.isOk()).toBe(true);
+      const customStream = customResult.unwrap();
+      expect(customStream.chunks).toHaveLength(4);
+      expect(customStream.totalSize).toBe(48);
+
+      // Error case - source not found
+      const notFoundResult = await useCase.execute({ source: 'not-found' });
+      expect(notFoundResult.isErr()).toBe(true);
+      expect(notFoundResult.unwrapErr()).toEqual({ code: 'SOURCE_NOT_FOUND' });
+
+      // Error case - stream error
+      const errorResult = await useCase.execute({ source: 'error' });
+      expect(errorResult.isErr()).toBe(true);
+      expect(errorResult.unwrapErr()).toEqual({ code: 'STREAM_ERROR' });
+    });
+  });
+});

core/shared/application/ErrorReporter.test.ts

@@ -0,0 +1,366 @@
+import { describe, it, expect } from 'vitest';
+import { ErrorReporter } from './ErrorReporter';
+
+describe('ErrorReporter', () => {
+  describe('ErrorReporter interface', () => {
+    it('should have report method', () => {
+      const errors: Array<{ error: Error; context?: unknown }> = [];
+
+      const reporter: ErrorReporter = {
+        report: (error: Error, context?: unknown) => {
+          errors.push({ error, context });
+        }
+      };
+
+      const testError = new Error('Test error');
+      reporter.report(testError, { userId: 123 });
+
+      expect(errors).toHaveLength(1);
+      expect(errors[0].error).toBe(testError);
+      expect(errors[0].context).toEqual({ userId: 123 });
+    });
+
+    it('should support reporting without context', () => {
+      const errors: Error[] = [];
+
+      const reporter: ErrorReporter = {
+        report: (error: Error) => {
+          errors.push(error);
+        }
+      };
+
+      const testError = new Error('Test error');
+      reporter.report(testError);
+
+      expect(errors).toHaveLength(1);
+      expect(errors[0]).toBe(testError);
+    });
+
+    it('should support different error types', () => {
+      const errors: Array<{ error: Error; context?: unknown }> = [];
+
+      const reporter: ErrorReporter = {
+        report: (error: Error, context?: unknown) => {
+          errors.push({ error, context });
+        }
+      };
+
+      // Standard Error
+      const standardError = new Error('Standard error');
+      reporter.report(standardError, { type: 'standard' });
+
+      // Custom Error
+      class CustomError extends Error {
+        constructor(message: string, public code: string) {
+          super(message);
+          this.name = 'CustomError';
+        }
+      }
+      const customError = new CustomError('Custom error', 'CUSTOM_CODE');
+      reporter.report(customError, { type: 'custom' });
+
+      // TypeError
+      const typeError = new TypeError('Type error');
+      reporter.report(typeError, { type: 'type' });
+
+      expect(errors).toHaveLength(3);
+      expect(errors[0].error).toBe(standardError);
+      expect(errors[1].error).toBe(customError);
+      expect(errors[2].error).toBe(typeError);
+    });
+
+    it('should support complex context objects', () => {
+      const errors: Array<{ error: Error; context?: unknown }> = [];
+
+      const reporter: ErrorReporter = {
+        report: (error: Error, context?: unknown) => {
+          errors.push({ error, context });
+        }
+      };
+
+      const complexContext = {
+        user: {
+          id: 'user-123',
+          name: 'John Doe',
+          email: 'john@example.com'
+        },
+        request: {
+          method: 'POST',
+          url: '/api/users',
+          headers: {
+            'content-type': 'application/json',
+            'authorization': 'Bearer token'
+          }
+        },
+        timestamp: new Date('2024-01-01T12:00:00Z'),
+        metadata: {
+          retryCount: 3,
+          timeout: 5000
+        }
+      };
+
+      const error = new Error('Request failed');
+      reporter.report(error, complexContext);
+
+      expect(errors).toHaveLength(1);
+      expect(errors[0].error).toBe(error);
+      expect(errors[0].context).toEqual(complexContext);
+    });
+  });
+
+  describe('ErrorReporter behavior', () => {
+    it('should support logging error with stack trace', () => {
+      const logs: Array<{ message: string; stack?: string; context?: unknown }> = [];
+
+      const reporter: ErrorReporter = {
+        report: (error: Error, context?: unknown) => {
+          logs.push({
+            message: error.message,
+            stack: error.stack,
+            context
+          });
+        }
+      };
+
+      const error = new Error('Database connection failed');
+      reporter.report(error, { retryCount: 3 });
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].message).toBe('Database connection failed');
+      expect(logs[0].stack).toBeDefined();
+      expect(logs[0].context).toEqual({ retryCount: 3 });
+    });
+
+    it('should support error aggregation', () => {
+      const errorCounts: Record<string, number> = {};
+
+      const reporter: ErrorReporter = {
+        report: (error: Error) => {
+          const errorType = error.name || 'Unknown';
+          errorCounts[errorType] = (errorCounts[errorType] || 0) + 1;
+        }
+      };
+
+      const error1 = new Error('Error 1');
+      const error2 = new TypeError('Type error');
+      const error3 = new Error('Error 2');
+      const error4 = new TypeError('Another type error');
+
+      reporter.report(error1);
+      reporter.report(error2);
+      reporter.report(error3);
+      reporter.report(error4);
+
+      expect(errorCounts['Error']).toBe(2);
+      expect(errorCounts['TypeError']).toBe(2);
+    });
+
+    it('should support error filtering', () => {
+      const criticalErrors: Error[] = [];
+      const warnings: Error[] = [];
+
+      const reporter: ErrorReporter = {
+        report: (error: Error, context?: unknown) => {
+          const isCritical = context && typeof context === 'object' && 'severity' in context && 
+                            (context as { severity: string }).severity === 'critical';
+          
+          if (isCritical) {
+            criticalErrors.push(error);
+          } else {
+            warnings.push(error);
+          }
+        }
+      };
+
+      const criticalError = new Error('Critical failure');
+      const warningError = new Error('Warning');
+
+      reporter.report(criticalError, { severity: 'critical' });
+      reporter.report(warningError, { severity: 'warning' });
+
+      expect(criticalErrors).toHaveLength(1);
+      expect(criticalErrors[0]).toBe(criticalError);
+      expect(warnings).toHaveLength(1);
+      expect(warnings[0]).toBe(warningError);
+    });
+
+    it('should support error enrichment', () => {
+      const enrichedErrors: Array<{ error: Error; enrichedContext: unknown }> = [];
+
+      const reporter: ErrorReporter = {
+        report: (error: Error, context?: unknown) => {
+          const enrichedContext: Record<string, unknown> = {
+            errorName: error.name,
+            errorMessage: error.message,
+            timestamp: new Date().toISOString(),
+            environment: process.env.NODE_ENV || 'development'
+          };
+          
+          if (context && typeof context === 'object') {
+            Object.assign(enrichedContext, context);
+          }
+
+          enrichedErrors.push({ error, enrichedContext });
+        }
+      };
+
+      const error = new Error('Something went wrong');
+      reporter.report(error, { userId: 'user-123', action: 'login' });
+
+      expect(enrichedErrors).toHaveLength(1);
+      expect(enrichedErrors[0].error).toBe(error);
+      expect(enrichedErrors[0].enrichedContext).toMatchObject({
+        userId: 'user-123',
+        action: 'login',
+        errorName: 'Error',
+        errorMessage: 'Something went wrong',
+        environment: 'development'
+      });
+    });
+
+    it('should support error deduplication', () => {
+      const uniqueErrors: Error[] = [];
+      const seenMessages = new Set<string>();
+
+      const reporter: ErrorReporter = {
+        report: (error: Error) => {
+          if (!seenMessages.has(error.message)) {
+            uniqueErrors.push(error);
+            seenMessages.add(error.message);
+          }
+        }
+      };
+
+      const error1 = new Error('Duplicate error');
+      const error2 = new Error('Duplicate error');
+      const error3 = new Error('Unique error');
+
+      reporter.report(error1);
+      reporter.report(error2);
+      reporter.report(error3);
+
+      expect(uniqueErrors).toHaveLength(2);
+      expect(uniqueErrors[0].message).toBe('Duplicate error');
+      expect(uniqueErrors[1].message).toBe('Unique error');
+    });
+
+    it('should support error rate limiting', () => {
+      const errors: Error[] = [];
+      let errorCount = 0;
+      const rateLimit = 5;
+
+      const reporter: ErrorReporter = {
+        report: (error: Error) => {
+          errorCount++;
+          if (errorCount <= rateLimit) {
+            errors.push(error);
+          }
+          // Silently drop errors beyond rate limit
+        }
+      };
+
+      // Report 10 errors
+      for (let i = 0; i < 10; i++) {
+        reporter.report(new Error(`Error ${i}`));
+      }
+
+      expect(errors).toHaveLength(rateLimit);
+      expect(errorCount).toBe(10);
+    });
+  });
+
+  describe('ErrorReporter implementation patterns', () => {
+    it('should support console logger implementation', () => {
+      const consoleErrors: string[] = [];
+      const originalConsoleError = console.error;
+
+      // Mock console.error
+      console.error = (...args: unknown[]) => consoleErrors.push(args.join(' '));
+
+      const consoleReporter: ErrorReporter = {
+        report: (error: Error, context?: unknown) => {
+          console.error('Error:', error.message, 'Context:', context);
+        }
+      };
+
+      const error = new Error('Test error');
+      consoleReporter.report(error, { userId: 123 });
+
+      // Restore console.error
+      console.error = originalConsoleError;
+
+      expect(consoleErrors).toHaveLength(1);
+      expect(consoleErrors[0]).toContain('Error:');
+      expect(consoleErrors[0]).toContain('Test error');
+      expect(consoleErrors[0]).toContain('Context:');
+    });
+
+    it('should support file logger implementation', () => {
+      const fileLogs: Array<{ timestamp: string; error: string; context?: unknown }> = [];
+
+      const fileReporter: ErrorReporter = {
+        report: (error: Error, context?: unknown) => {
+          fileLogs.push({
+            timestamp: new Date().toISOString(),
+            error: error.message,
+            context
+          });
+        }
+      };
+
+      const error = new Error('File error');
+      fileReporter.report(error, { file: 'test.txt', line: 42 });
+
+      expect(fileLogs).toHaveLength(1);
+      expect(fileLogs[0].error).toBe('File error');
+      expect(fileLogs[0].context).toEqual({ file: 'test.txt', line: 42 });
+    });
+
+    it('should support remote reporter implementation', async () => {
+      const remoteErrors: Array<{ error: string; context?: unknown }> = [];
+
+      const remoteReporter: ErrorReporter = {
+        report: async (error: Error, context?: unknown) => {
+          remoteErrors.push({ error: error.message, context });
+          await new Promise(resolve => setTimeout(resolve, 1));
+        }
+      };
+
+      const error = new Error('Remote error');
+      await remoteReporter.report(error, { endpoint: '/api/data' });
+
+      expect(remoteErrors).toHaveLength(1);
+      expect(remoteErrors[0].error).toBe('Remote error');
+      expect(remoteErrors[0].context).toEqual({ endpoint: '/api/data' });
+    });
+
+    it('should support batch error reporting', () => {
+      const batchErrors: Error[] = [];
+      const batchSize = 3;
+      let currentBatch: Error[] = [];
+
+      const reporter: ErrorReporter = {
+        report: (error: Error) => {
+          currentBatch.push(error);
+
+          if (currentBatch.length >= batchSize) {
+            batchErrors.push(...currentBatch);
+            currentBatch = [];
+          }
+        }
+      };
+
+      // Report 7 errors
+      for (let i = 0; i < 7; i++) {
+        reporter.report(new Error(`Error ${i}`));
+      }
+
+      // Add remaining errors
+      if (currentBatch.length > 0) {
+        batchErrors.push(...currentBatch);
+      }
+
+      expect(batchErrors).toHaveLength(7);
+    });
+  });
+});

core/shared/application/Service.test.ts

@@ -0,0 +1,451 @@
+import { describe, it, expect } from 'vitest';
+import { ApplicationService, AsyncApplicationService, AsyncResultApplicationService } from './Service';
+import { Result } from '../domain/Result';
+import { ApplicationError } from '../errors/ApplicationError';
+
+describe('Service', () => {
+  describe('ApplicationService interface', () => {
+    it('should have optional serviceName property', () => {
+      const service: ApplicationService = {
+        serviceName: 'TestService'
+      };
+
+      expect(service.serviceName).toBe('TestService');
+    });
+
+    it('should work without serviceName', () => {
+      const service: ApplicationService = {};
+
+      expect(service.serviceName).toBeUndefined();
+    });
+
+    it('should support different service implementations', () => {
+      const service1: ApplicationService = { serviceName: 'Service1' };
+      const service2: ApplicationService = { serviceName: 'Service2' };
+      const service3: ApplicationService = {};
+
+      expect(service1.serviceName).toBe('Service1');
+      expect(service2.serviceName).toBe('Service2');
+      expect(service3.serviceName).toBeUndefined();
+    });
+  });
+
+  describe('AsyncApplicationService interface', () => {
+    it('should have execute method returning Promise<Output>', async () => {
+      const service: AsyncApplicationService<string, number> = {
+        execute: async (input: string) => input.length
+      };
+
+      const result = await service.execute('test');
+      expect(result).toBe(4);
+    });
+
+    it('should support different input and output types', async () => {
+      const stringService: AsyncApplicationService<string, string> = {
+        execute: async (input: string) => input.toUpperCase()
+      };
+
+      const objectService: AsyncApplicationService<{ x: number; y: number }, number> = {
+        execute: async (input) => input.x + input.y
+      };
+
+      const arrayService: AsyncApplicationService<number[], number[]> = {
+        execute: async (input) => input.map(x => x * 2)
+      };
+
+      expect(await stringService.execute('hello')).toBe('HELLO');
+      expect(await objectService.execute({ x: 3, y: 4 })).toBe(7);
+      expect(await arrayService.execute([1, 2, 3])).toEqual([2, 4, 6]);
+    });
+
+    it('should support async operations with delays', async () => {
+      const service: AsyncApplicationService<string, string> = {
+        execute: async (input: string) => {
+          await new Promise(resolve => setTimeout(resolve, 10));
+          return `Processed: ${input}`;
+        }
+      };
+
+      const start = Date.now();
+      const result = await service.execute('test');
+      const elapsed = Date.now() - start;
+
+      expect(result).toBe('Processed: test');
+      expect(elapsed).toBeGreaterThanOrEqual(10);
+    });
+
+    it('should support complex async operations', async () => {
+      interface FetchUserInput {
+        userId: string;
+        includePosts?: boolean;
+      }
+
+      interface UserWithPosts {
+        id: string;
+        name: string;
+        email: string;
+        posts: Array<{ id: string; title: string; content: string }>;
+      }
+
+      const userService: AsyncApplicationService<FetchUserInput, UserWithPosts> = {
+        execute: async (input: FetchUserInput) => {
+          // Simulate async database fetch
+          await new Promise(resolve => setTimeout(resolve, 5));
+
+          const user: UserWithPosts = {
+            id: input.userId,
+            name: 'John Doe',
+            email: 'john@example.com',
+            posts: []
+          };
+
+          if (input.includePosts) {
+            user.posts = [
+              { id: 'post-1', title: 'First Post', content: 'Content 1' },
+              { id: 'post-2', title: 'Second Post', content: 'Content 2' }
+            ];
+          }
+
+          return user;
+        }
+      };
+
+      const userWithPosts = await userService.execute({
+        userId: 'user-123',
+        includePosts: true
+      });
+
+      expect(userWithPosts.id).toBe('user-123');
+      expect(userWithPosts.posts).toHaveLength(2);
+
+      const userWithoutPosts = await userService.execute({
+        userId: 'user-456',
+        includePosts: false
+      });
+
+      expect(userWithoutPosts.id).toBe('user-456');
+      expect(userWithoutPosts.posts).toHaveLength(0);
+    });
+  });
+
+  describe('AsyncResultApplicationService interface', () => {
+    it('should have execute method returning Promise<Result>', async () => {
+      const service: AsyncResultApplicationService<string, number, string> = {
+        execute: async (input: string) => {
+          if (input.length === 0) {
+            return Result.err('Input cannot be empty');
+          }
+          return Result.ok(input.length);
+        }
+      };
+
+      const successResult = await service.execute('test');
+      expect(successResult.isOk()).toBe(true);
+      expect(successResult.unwrap()).toBe(4);
+
+      const errorResult = await service.execute('');
+      expect(errorResult.isErr()).toBe(true);
+      expect(errorResult.unwrapErr()).toBe('Input cannot be empty');
+    });
+
+    it('should support validation logic', async () => {
+      interface ValidationResult {
+        isValid: boolean;
+        errors: string[];
+      }
+
+      const validator: AsyncResultApplicationService<string, ValidationResult, string> = {
+        execute: async (input: string) => {
+          const errors: string[] = [];
+
+          if (input.length < 3) {
+            errors.push('Must be at least 3 characters');
+          }
+
+          if (!input.match(/^[a-zA-Z]+$/)) {
+            errors.push('Must contain only letters');
+          }
+
+          if (errors.length > 0) {
+            return Result.err(errors.join(', '));
+          }
+
+          return Result.ok({ isValid: true, errors: [] });
+        }
+      };
+
+      const validResult = await validator.execute('Hello');
+      expect(validResult.isOk()).toBe(true);
+      expect(validResult.unwrap()).toEqual({ isValid: true, errors: [] });
+
+      const invalidResult = await validator.execute('ab');
+      expect(invalidResult.isErr()).toBe(true);
+      expect(invalidResult.unwrapErr()).toBe('Must be at least 3 characters');
+    });
+
+    it('should support complex business rules', async () => {
+      interface ProcessOrderInput {
+        items: Array<{ productId: string; quantity: number; price: number }>;
+        customerType: 'regular' | 'premium' | 'vip';
+        hasCoupon: boolean;
+      }
+
+      interface OrderResult {
+        orderId: string;
+        subtotal: number;
+        discount: number;
+        total: number;
+        status: 'processed' | 'pending' | 'failed';
+      }
+
+      const orderProcessor: AsyncResultApplicationService<ProcessOrderInput, OrderResult, string> = {
+        execute: async (input: ProcessOrderInput) => {
+          // Calculate subtotal
+          const subtotal = input.items.reduce((sum, item) => sum + (item.quantity * item.price), 0);
+
+          if (subtotal <= 0) {
+            return Result.err('Order must have items with positive prices');
+          }
+
+          // Calculate discount
+          let discount = 0;
+
+          // Customer type discount
+          switch (input.customerType) {
+            case 'premium':
+              discount += subtotal * 0.1;
+              break;
+            case 'vip':
+              discount += subtotal * 0.2;
+              break;
+          }
+
+          // Coupon discount
+          if (input.hasCoupon) {
+            discount += subtotal * 0.05;
+          }
+
+          const total = subtotal - discount;
+
+          const orderResult: OrderResult = {
+            orderId: `order-${Date.now()}`,
+            subtotal,
+            discount,
+            total,
+            status: 'processed'
+          };
+
+          return Result.ok(orderResult);
+        }
+      };
+
+      // Success case - VIP with coupon
+      const vipWithCoupon = await orderProcessor.execute({
+        items: [
+          { productId: 'prod-1', quantity: 2, price: 100 },
+          { productId: 'prod-2', quantity: 1, price: 50 }
+        ],
+        customerType: 'vip',
+        hasCoupon: true
+      });
+
+      expect(vipWithCoupon.isOk()).toBe(true);
+      const order1 = vipWithCoupon.unwrap();
+      expect(order1.subtotal).toBe(250); // 2*100 + 1*50
+      expect(order1.discount).toBe(62.5); // 250 * 0.2 + 250 * 0.05
+      expect(order1.total).toBe(187.5); // 250 - 62.5
+
+      // Success case - Regular without coupon
+      const regularWithoutCoupon = await orderProcessor.execute({
+        items: [{ productId: 'prod-1', quantity: 1, price: 100 }],
+        customerType: 'regular',
+        hasCoupon: false
+      });
+
+      expect(regularWithoutCoupon.isOk()).toBe(true);
+      const order2 = regularWithoutCoupon.unwrap();
+      expect(order2.subtotal).toBe(100);
+      expect(order2.discount).toBe(0);
+      expect(order2.total).toBe(100);
+
+      // Error case - Empty order
+      const emptyOrder = await orderProcessor.execute({
+        items: [],
+        customerType: 'regular',
+        hasCoupon: false
+      });
+
+      expect(emptyOrder.isErr()).toBe(true);
+      expect(emptyOrder.unwrapErr()).toBe('Order must have items with positive prices');
+    });
+
+    it('should support async operations with delays', async () => {
+      interface ProcessBatchInput {
+        items: Array<{ id: string; data: string }>;
+        delayMs?: number;
+      }
+
+      interface BatchResult {
+        processed: number;
+        failed: number;
+        results: Array<{ id: string; status: 'success' | 'failed'; message?: string }>;
+      }
+
+      const batchProcessor: AsyncResultApplicationService<ProcessBatchInput, BatchResult, string> = {
+        execute: async (input: ProcessBatchInput) => {
+          if (input.items.length === 0) {
+            return Result.err('Empty batch');
+          }
+
+          const delay = input.delayMs || 10;
+          const results: Array<{ id: string; status: 'success' | 'failed'; message?: string }> = [];
+          let processed = 0;
+          let failed = 0;
+
+          for (const item of input.items) {
+            // Simulate async processing with delay
+            await new Promise(resolve => setTimeout(resolve, delay));
+
+            // Simulate some failures
+            if (item.id === 'fail-1' || item.id === 'fail-2') {
+              results.push({ id: item.id, status: 'failed', message: 'Processing failed' });
+              failed++;
+            } else {
+              results.push({ id: item.id, status: 'success' });
+              processed++;
+            }
+          }
+
+          return Result.ok({
+            processed,
+            failed,
+            results
+          });
+        }
+      };
+
+      // Success case
+      const successResult = await batchProcessor.execute({
+        items: [
+          { id: 'item-1', data: 'data1' },
+          { id: 'item-2', data: 'data2' },
+          { id: 'item-3', data: 'data3' }
+        ],
+        delayMs: 5
+      });
+
+      expect(successResult.isOk()).toBe(true);
+      const batchResult = successResult.unwrap();
+      expect(batchResult.processed).toBe(3);
+      expect(batchResult.failed).toBe(0);
+      expect(batchResult.results).toHaveLength(3);
+
+      // Mixed success/failure case
+      const mixedResult = await batchProcessor.execute({
+        items: [
+          { id: 'item-1', data: 'data1' },
+          { id: 'fail-1', data: 'data2' },
+          { id: 'item-3', data: 'data3' },
+          { id: 'fail-2', data: 'data4' }
+        ],
+        delayMs: 5
+      });
+
+      expect(mixedResult.isOk()).toBe(true);
+      const mixedBatchResult = mixedResult.unwrap();
+      expect(mixedBatchResult.processed).toBe(2);
+      expect(mixedBatchResult.failed).toBe(2);
+      expect(mixedBatchResult.results).toHaveLength(4);
+
+      // Error case - empty batch
+      const emptyResult = await batchProcessor.execute({ items: [] });
+      expect(emptyResult.isErr()).toBe(true);
+      expect(emptyResult.unwrapErr()).toBe('Empty batch');
+    });
+
+    it('should support error handling with ApplicationError', async () => {
+      interface ProcessPaymentInput {
+        amount: number;
+        currency: string;
+      }
+
+      interface PaymentReceipt {
+        receiptId: string;
+        amount: number;
+        currency: string;
+        status: 'completed' | 'failed';
+      }
+
+      const paymentProcessor: AsyncResultApplicationService<ProcessPaymentInput, PaymentReceipt, ApplicationError> = {
+        execute: async (input: ProcessPaymentInput) => {
+          // Validate amount
+          if (input.amount <= 0) {
+            return Result.err({
+              type: 'application',
+              context: 'payment',
+              kind: 'validation',
+              message: 'Amount must be positive'
+            } as ApplicationError);
+          }
+
+          // Validate currency
+          const supportedCurrencies = ['USD', 'EUR', 'GBP'];
+          if (!supportedCurrencies.includes(input.currency)) {
+            return Result.err({
+              type: 'application',
+              context: 'payment',
+              kind: 'validation',
+              message: `Currency ${input.currency} is not supported`
+            } as ApplicationError);
+          }
+
+          // Simulate payment processing
+          const receipt: PaymentReceipt = {
+            receiptId: `receipt-${Date.now()}`,
+            amount: input.amount,
+            currency: input.currency,
+            status: 'completed'
+          };
+
+          return Result.ok(receipt);
+        }
+      };
+
+      // Success case
+      const successResult = await paymentProcessor.execute({
+        amount: 100,
+        currency: 'USD'
+      });
+
+      expect(successResult.isOk()).toBe(true);
+      const receipt = successResult.unwrap();
+      expect(receipt.amount).toBe(100);
+      expect(receipt.currency).toBe('USD');
+      expect(receipt.status).toBe('completed');
+
+      // Error case - invalid amount
+      const invalidAmountResult = await paymentProcessor.execute({
+        amount: -50,
+        currency: 'USD'
+      });
+
+      expect(invalidAmountResult.isErr()).toBe(true);
+      const error1 = invalidAmountResult.unwrapErr();
+      expect(error1.type).toBe('application');
+      expect(error1.kind).toBe('validation');
+      expect(error1.message).toBe('Amount must be positive');
+
+      // Error case - invalid currency
+      const invalidCurrencyResult = await paymentProcessor.execute({
+        amount: 100,
+        currency: 'JPY'
+      });
+
+      expect(invalidCurrencyResult.isErr()).toBe(true);
+      const error2 = invalidCurrencyResult.unwrapErr();
+      expect(error2.type).toBe('application');
+      expect(error2.kind).toBe('validation');
+      expect(error2.message).toBe('Currency JPY is not supported');
+    });
+  });
+});

core/shared/application/UseCase.test.ts

@@ -0,0 +1,324 @@
+import { describe, it, expect } from 'vitest';
+import { UseCase } from './UseCase';
+import { Result } from '../domain/Result';
+import { ApplicationErrorCode } from '../errors/ApplicationErrorCode';
+
+describe('UseCase', () => {
+  describe('UseCase interface', () => {
+    it('should have execute method returning Promise<Result>', async () => {
+      // Concrete implementation for testing
+      class TestUseCase implements UseCase<{ value: number }, string, 'INVALID_VALUE'> {
+        async execute(input: { value: number }): Promise<Result<string, ApplicationErrorCode<'INVALID_VALUE'>>> {
+          if (input.value < 0) {
+            return Result.err({ code: 'INVALID_VALUE' });
+          }
+          return Result.ok(`Value: ${input.value}`);
+        }
+      }
+
+      const useCase = new TestUseCase();
+
+      const successResult = await useCase.execute({ value: 42 });
+      expect(successResult.isOk()).toBe(true);
+      expect(successResult.unwrap()).toBe('Value: 42');
+
+      const errorResult = await useCase.execute({ value: -1 });
+      expect(errorResult.isErr()).toBe(true);
+      expect(errorResult.unwrapErr()).toEqual({ code: 'INVALID_VALUE' });
+    });
+
+    it('should support different input types', async () => {
+      interface CreateUserInput {
+        name: string;
+        email: string;
+      }
+
+      interface UserDTO {
+        id: string;
+        name: string;
+        email: string;
+      }
+
+      type CreateUserErrorCode = 'INVALID_EMAIL' | 'USER_ALREADY_EXISTS';
+
+      class CreateUserUseCase implements UseCase<CreateUserInput, UserDTO, CreateUserErrorCode> {
+        async execute(input: CreateUserInput): Promise<Result<UserDTO, ApplicationErrorCode<CreateUserErrorCode>>> {
+          if (!input.email.includes('@')) {
+            return Result.err({ code: 'INVALID_EMAIL' });
+          }
+
+          // Simulate user creation
+          const user: UserDTO = {
+            id: `user-${Date.now()}`,
+            name: input.name,
+            email: input.email
+          };
+
+          return Result.ok(user);
+        }
+      }
+
+      const useCase = new CreateUserUseCase();
+
+      const successResult = await useCase.execute({
+        name: 'John Doe',
+        email: 'john@example.com'
+      });
+
+      expect(successResult.isOk()).toBe(true);
+      const user = successResult.unwrap();
+      expect(user.name).toBe('John Doe');
+      expect(user.email).toBe('john@example.com');
+      expect(user.id).toMatch(/^user-\d+$/);
+
+      const errorResult = await useCase.execute({
+        name: 'John Doe',
+        email: 'invalid-email'
+      });
+
+      expect(errorResult.isErr()).toBe(true);
+      expect(errorResult.unwrapErr()).toEqual({ code: 'INVALID_EMAIL' });
+    });
+
+    it('should support complex error codes', async () => {
+      interface ProcessPaymentInput {
+        amount: number;
+        currency: string;
+        paymentMethod: 'credit_card' | 'paypal' | 'bank_transfer';
+      }
+
+      interface PaymentReceipt {
+        receiptId: string;
+        amount: number;
+        currency: string;
+        status: 'completed' | 'pending' | 'failed';
+      }
+
+      type ProcessPaymentErrorCode =
+        | 'INSUFFICIENT_FUNDS'
+        | 'INVALID_CURRENCY'
+        | 'PAYMENT_METHOD_NOT_SUPPORTED'
+        | 'NETWORK_ERROR';
+
+      class ProcessPaymentUseCase implements UseCase<ProcessPaymentInput, PaymentReceipt, ProcessPaymentErrorCode> {
+        async execute(input: ProcessPaymentInput): Promise<Result<PaymentReceipt, ApplicationErrorCode<ProcessPaymentErrorCode>>> {
+          // Validate currency
+          const supportedCurrencies = ['USD', 'EUR', 'GBP'];
+          if (!supportedCurrencies.includes(input.currency)) {
+            return Result.err({ code: 'INVALID_CURRENCY' });
+          }
+
+          // Validate payment method
+          const supportedMethods = ['credit_card', 'paypal'];
+          if (!supportedMethods.includes(input.paymentMethod)) {
+            return Result.err({ code: 'PAYMENT_METHOD_NOT_SUPPORTED' });
+          }
+
+          // Simulate payment processing
+          if (input.amount > 10000) {
+            return Result.err({ code: 'INSUFFICIENT_FUNDS' });
+          }
+
+          const receipt: PaymentReceipt = {
+            receiptId: `receipt-${Date.now()}`,
+            amount: input.amount,
+            currency: input.currency,
+            status: 'completed'
+          };
+
+          return Result.ok(receipt);
+        }
+      }
+
+      const useCase = new ProcessPaymentUseCase();
+
+      // Success case
+      const successResult = await useCase.execute({
+        amount: 100,
+        currency: 'USD',
+        paymentMethod: 'credit_card'
+      });
+
+      expect(successResult.isOk()).toBe(true);
+      const receipt = successResult.unwrap();
+      expect(receipt.amount).toBe(100);
+      expect(receipt.currency).toBe('USD');
+      expect(receipt.status).toBe('completed');
+
+      // Error case - invalid currency
+      const currencyError = await useCase.execute({
+        amount: 100,
+        currency: 'JPY',
+        paymentMethod: 'credit_card'
+      });
+
+      expect(currencyError.isErr()).toBe(true);
+      expect(currencyError.unwrapErr()).toEqual({ code: 'INVALID_CURRENCY' });
+
+      // Error case - unsupported payment method
+      const methodError = await useCase.execute({
+        amount: 100,
+        currency: 'USD',
+        paymentMethod: 'bank_transfer'
+      });
+
+      expect(methodError.isErr()).toBe(true);
+      expect(methodError.unwrapErr()).toEqual({ code: 'PAYMENT_METHOD_NOT_SUPPORTED' });
+
+      // Error case - insufficient funds
+      const fundsError = await useCase.execute({
+        amount: 15000,
+        currency: 'USD',
+        paymentMethod: 'credit_card'
+      });
+
+      expect(fundsError.isErr()).toBe(true);
+      expect(fundsError.unwrapErr()).toEqual({ code: 'INSUFFICIENT_FUNDS' });
+    });
+
+    it('should support void success type', async () => {
+      interface DeleteUserInput {
+        userId: string;
+      }
+
+      type DeleteUserErrorCode = 'USER_NOT_FOUND' | 'INSUFFICIENT_PERMISSIONS';
+
+      class DeleteUserUseCase implements UseCase<DeleteUserInput, void, DeleteUserErrorCode> {
+        async execute(input: DeleteUserInput): Promise<Result<void, ApplicationErrorCode<DeleteUserErrorCode>>> {
+          if (input.userId === 'not-found') {
+            return Result.err({ code: 'USER_NOT_FOUND' });
+          }
+
+          if (input.userId === 'no-permission') {
+            return Result.err({ code: 'INSUFFICIENT_PERMISSIONS' });
+          }
+
+          // Simulate deletion
+          return Result.ok(undefined);
+        }
+      }
+
+      const useCase = new DeleteUserUseCase();
+
+      const successResult = await useCase.execute({ userId: 'user-123' });
+      expect(successResult.isOk()).toBe(true);
+      expect(successResult.unwrap()).toBeUndefined();
+
+      const notFoundResult = await useCase.execute({ userId: 'not-found' });
+      expect(notFoundResult.isErr()).toBe(true);
+      expect(notFoundResult.unwrapErr()).toEqual({ code: 'USER_NOT_FOUND' });
+
+      const permissionResult = await useCase.execute({ userId: 'no-permission' });
+      expect(permissionResult.isErr()).toBe(true);
+      expect(permissionResult.unwrapErr()).toEqual({ code: 'INSUFFICIENT_PERMISSIONS' });
+    });
+
+    it('should support complex success types', async () => {
+      interface SearchInput {
+        query: string;
+        filters?: {
+          category?: string;
+          priceRange?: { min: number; max: number };
+          inStock?: boolean;
+        };
+        page?: number;
+        limit?: number;
+      }
+
+      interface SearchResult {
+        items: Array<{
+          id: string;
+          name: string;
+          price: number;
+          category: string;
+          inStock: boolean;
+        }>;
+        total: number;
+        page: number;
+        totalPages: number;
+      }
+
+      type SearchErrorCode = 'INVALID_QUERY' | 'NO_RESULTS';
+
+      class SearchUseCase implements UseCase<SearchInput, SearchResult, SearchErrorCode> {
+        async execute(input: SearchInput): Promise<Result<SearchResult, ApplicationErrorCode<SearchErrorCode>>> {
+          if (!input.query || input.query.length < 2) {
+            return Result.err({ code: 'INVALID_QUERY' });
+          }
+
+          // Simulate search results
+          const items = [
+            { id: '1', name: 'Product A', price: 100, category: 'electronics', inStock: true },
+            { id: '2', name: 'Product B', price: 200, category: 'electronics', inStock: false },
+            { id: '3', name: 'Product C', price: 150, category: 'clothing', inStock: true }
+          ];
+
+          const filteredItems = items.filter(item => {
+            if (input.filters?.category && item.category !== input.filters.category) {
+              return false;
+            }
+            if (input.filters?.priceRange) {
+              if (item.price < input.filters.priceRange.min || item.price > input.filters.priceRange.max) {
+                return false;
+              }
+            }
+            if (input.filters?.inStock !== undefined && item.inStock !== input.filters.inStock) {
+              return false;
+            }
+            return true;
+          });
+
+          if (filteredItems.length === 0) {
+            return Result.err({ code: 'NO_RESULTS' });
+          }
+
+          const page = input.page || 1;
+          const limit = input.limit || 10;
+          const start = (page - 1) * limit;
+          const end = start + limit;
+          const paginatedItems = filteredItems.slice(start, end);
+
+          const result: SearchResult = {
+            items: paginatedItems,
+            total: filteredItems.length,
+            page,
+            totalPages: Math.ceil(filteredItems.length / limit)
+          };
+
+          return Result.ok(result);
+        }
+      }
+
+      const useCase = new SearchUseCase();
+
+      // Success case
+      const successResult = await useCase.execute({
+        query: 'product',
+        filters: { category: 'electronics' },
+        page: 1,
+        limit: 10
+      });
+
+      expect(successResult.isOk()).toBe(true);
+      const searchResult = successResult.unwrap();
+      expect(searchResult.items).toHaveLength(2);
+      expect(searchResult.total).toBe(2);
+      expect(searchResult.page).toBe(1);
+      expect(searchResult.totalPages).toBe(1);
+
+      // Error case - invalid query
+      const invalidQueryResult = await useCase.execute({ query: 'a' });
+      expect(invalidQueryResult.isErr()).toBe(true);
+      expect(invalidQueryResult.unwrapErr()).toEqual({ code: 'INVALID_QUERY' });
+
+      // Error case - no results
+      const noResultsResult = await useCase.execute({
+        query: 'product',
+        filters: { category: 'nonexistent' }
+      });
+
+      expect(noResultsResult.isErr()).toBe(true);
+      expect(noResultsResult.unwrapErr()).toEqual({ code: 'NO_RESULTS' });
+    });
+  });
+});

core/shared/application/UseCaseOutputPort.test.ts

@@ -0,0 +1,431 @@
+import { describe, it, expect } from 'vitest';
+import { UseCaseOutputPort } from './UseCaseOutputPort';
+
+describe('UseCaseOutputPort', () => {
+  describe('UseCaseOutputPort interface', () => {
+    it('should have present method', () => {
+      const presentedData: unknown[] = [];
+
+      const outputPort: UseCaseOutputPort<string> = {
+        present: (data: string) => {
+          presentedData.push(data);
+        }
+      };
+
+      outputPort.present('test data');
+
+      expect(presentedData).toHaveLength(1);
+      expect(presentedData[0]).toBe('test data');
+    });
+
+    it('should support different data types', () => {
+      const presentedData: Array<{ type: string; data: unknown }> = [];
+
+      const outputPort: UseCaseOutputPort<unknown> = {
+        present: (data: unknown) => {
+          presentedData.push({ type: typeof data, data });
+        }
+      };
+
+      outputPort.present('string data');
+      outputPort.present(42);
+      outputPort.present({ id: 1, name: 'test' });
+      outputPort.present([1, 2, 3]);
+
+      expect(presentedData).toHaveLength(4);
+      expect(presentedData[0]).toEqual({ type: 'string', data: 'string data' });
+      expect(presentedData[1]).toEqual({ type: 'number', data: 42 });
+      expect(presentedData[2]).toEqual({ type: 'object', data: { id: 1, name: 'test' } });
+      expect(presentedData[3]).toEqual({ type: 'object', data: [1, 2, 3] });
+    });
+
+    it('should support complex data structures', () => {
+      interface UserDTO {
+        id: string;
+        name: string;
+        email: string;
+        profile: {
+          avatar: string;
+          bio: string;
+          preferences: {
+            theme: 'light' | 'dark';
+            notifications: boolean;
+          };
+        };
+        metadata: {
+          createdAt: Date;
+          updatedAt: Date;
+          lastLogin?: Date;
+        };
+      }
+
+      const presentedUsers: UserDTO[] = [];
+
+      const outputPort: UseCaseOutputPort<UserDTO> = {
+        present: (data: UserDTO) => {
+          presentedUsers.push(data);
+        }
+      };
+
+      const user: UserDTO = {
+        id: 'user-123',
+        name: 'John Doe',
+        email: 'john@example.com',
+        profile: {
+          avatar: 'avatar.jpg',
+          bio: 'Software developer',
+          preferences: {
+            theme: 'dark',
+            notifications: true
+          }
+        },
+        metadata: {
+          createdAt: new Date('2024-01-01'),
+          updatedAt: new Date('2024-01-02'),
+          lastLogin: new Date('2024-01-03')
+        }
+      };
+
+      outputPort.present(user);
+
+      expect(presentedUsers).toHaveLength(1);
+      expect(presentedUsers[0]).toEqual(user);
+    });
+
+    it('should support array data', () => {
+      const presentedArrays: number[][] = [];
+
+      const outputPort: UseCaseOutputPort<number[]> = {
+        present: (data: number[]) => {
+          presentedArrays.push(data);
+        }
+      };
+
+      outputPort.present([1, 2, 3]);
+      outputPort.present([4, 5, 6]);
+
+      expect(presentedArrays).toHaveLength(2);
+      expect(presentedArrays[0]).toEqual([1, 2, 3]);
+      expect(presentedArrays[1]).toEqual([4, 5, 6]);
+    });
+
+    it('should support null and undefined values', () => {
+      const presentedValues: unknown[] = [];
+
+      const outputPort: UseCaseOutputPort<unknown> = {
+        present: (data: unknown) => {
+          presentedValues.push(data);
+        }
+      };
+
+      outputPort.present(null);
+      outputPort.present(undefined);
+      outputPort.present('value');
+
+      expect(presentedValues).toHaveLength(3);
+      expect(presentedValues[0]).toBe(null);
+      expect(presentedValues[1]).toBe(undefined);
+      expect(presentedValues[2]).toBe('value');
+    });
+  });
+
+  describe('UseCaseOutputPort behavior', () => {
+    it('should support transformation before presentation', () => {
+      const presentedData: Array<{ transformed: string; original: string }> = [];
+
+      const outputPort: UseCaseOutputPort<string> = {
+        present: (data: string) => {
+          const transformed = data.toUpperCase();
+          presentedData.push({ transformed, original: data });
+        }
+      };
+
+      outputPort.present('hello');
+      outputPort.present('world');
+
+      expect(presentedData).toHaveLength(2);
+      expect(presentedData[0]).toEqual({ transformed: 'HELLO', original: 'hello' });
+      expect(presentedData[1]).toEqual({ transformed: 'WORLD', original: 'world' });
+    });
+
+    it('should support validation before presentation', () => {
+      const presentedData: string[] = [];
+      const validationErrors: string[] = [];
+
+      const outputPort: UseCaseOutputPort<string> = {
+        present: (data: string) => {
+          if (data.length === 0) {
+            validationErrors.push('Data cannot be empty');
+            return;
+          }
+
+          if (data.length > 100) {
+            validationErrors.push('Data exceeds maximum length');
+            return;
+          }
+
+          presentedData.push(data);
+        }
+      };
+
+      outputPort.present('valid data');
+      outputPort.present('');
+      outputPort.present('a'.repeat(101));
+      outputPort.present('another valid');
+
+      expect(presentedData).toHaveLength(2);
+      expect(presentedData[0]).toBe('valid data');
+      expect(presentedData[1]).toBe('another valid');
+      expect(validationErrors).toHaveLength(2);
+      expect(validationErrors[0]).toBe('Data cannot be empty');
+      expect(validationErrors[1]).toBe('Data exceeds maximum length');
+    });
+
+    it('should support pagination', () => {
+      interface PaginatedResult<T> {
+        items: T[];
+        total: number;
+        page: number;
+        totalPages: number;
+      }
+
+      const presentedPages: PaginatedResult<string>[] = [];
+
+      const outputPort: UseCaseOutputPort<PaginatedResult<string>> = {
+        present: (data: PaginatedResult<string>) => {
+          presentedPages.push(data);
+        }
+      };
+
+      const page1: PaginatedResult<string> = {
+        items: ['item-1', 'item-2', 'item-3'],
+        total: 10,
+        page: 1,
+        totalPages: 4
+      };
+
+      const page2: PaginatedResult<string> = {
+        items: ['item-4', 'item-5', 'item-6'],
+        total: 10,
+        page: 2,
+        totalPages: 4
+      };
+
+      outputPort.present(page1);
+      outputPort.present(page2);
+
+      expect(presentedPages).toHaveLength(2);
+      expect(presentedPages[0]).toEqual(page1);
+      expect(presentedPages[1]).toEqual(page2);
+    });
+
+    it('should support streaming presentation', () => {
+      const stream: string[] = [];
+
+      const outputPort: UseCaseOutputPort<string> = {
+        present: (data: string) => {
+          stream.push(data);
+        }
+      };
+
+      // Simulate streaming data
+      const chunks = ['chunk-1', 'chunk-2', 'chunk-3', 'chunk-4'];
+      chunks.forEach(chunk => outputPort.present(chunk));
+
+      expect(stream).toHaveLength(4);
+      expect(stream).toEqual(chunks);
+    });
+
+    it('should support error handling in presentation', () => {
+      const presentedData: string[] = [];
+      const presentationErrors: Error[] = [];
+
+      const outputPort: UseCaseOutputPort<string> = {
+        present: (data: string) => {
+          try {
+            // Simulate complex presentation logic that might fail
+            if (data === 'error') {
+              throw new Error('Presentation failed');
+            }
+            presentedData.push(data);
+          } catch (error) {
+            if (error instanceof Error) {
+              presentationErrors.push(error);
+            }
+          }
+        }
+      };
+
+      outputPort.present('valid-1');
+      outputPort.present('error');
+      outputPort.present('valid-2');
+
+      expect(presentedData).toHaveLength(2);
+      expect(presentedData[0]).toBe('valid-1');
+      expect(presentedData[1]).toBe('valid-2');
+      expect(presentationErrors).toHaveLength(1);
+      expect(presentationErrors[0].message).toBe('Presentation failed');
+    });
+  });
+
+  describe('UseCaseOutputPort implementation patterns', () => {
+    it('should support console presenter', () => {
+      const consoleOutputs: string[] = [];
+      const originalConsoleLog = console.log;
+
+      // Mock console.log
+      console.log = (...args: unknown[]) => consoleOutputs.push(args.join(' '));
+
+      const consolePresenter: UseCaseOutputPort<string> = {
+        present: (data: string) => {
+          console.log('Presented:', data);
+        }
+      };
+
+      consolePresenter.present('test data');
+
+      // Restore console.log
+      console.log = originalConsoleLog;
+
+      expect(consoleOutputs).toHaveLength(1);
+      expect(consoleOutputs[0]).toContain('Presented:');
+      expect(consoleOutputs[0]).toContain('test data');
+    });
+
+    it('should support HTTP response presenter', () => {
+      const responses: Array<{ status: number; body: unknown; headers?: Record<string, string> }> = [];
+
+      const httpResponsePresenter: UseCaseOutputPort<unknown> = {
+        present: (data: unknown) => {
+          responses.push({
+            status: 200,
+            body: data,
+            headers: {
+              'content-type': 'application/json'
+            }
+          });
+        }
+      };
+
+      httpResponsePresenter.present({ id: 1, name: 'test' });
+
+      expect(responses).toHaveLength(1);
+      expect(responses[0].status).toBe(200);
+      expect(responses[0].body).toEqual({ id: 1, name: 'test' });
+      expect(responses[0].headers).toEqual({ 'content-type': 'application/json' });
+    });
+
+    it('should support WebSocket presenter', () => {
+      const messages: Array<{ type: string; data: unknown; timestamp: string }> = [];
+
+      const webSocketPresenter: UseCaseOutputPort<unknown> = {
+        present: (data: unknown) => {
+          messages.push({
+            type: 'data',
+            data,
+            timestamp: new Date().toISOString()
+          });
+        }
+      };
+
+      webSocketPresenter.present({ event: 'user-joined', userId: 'user-123' });
+
+      expect(messages).toHaveLength(1);
+      expect(messages[0].type).toBe('data');
+      expect(messages[0].data).toEqual({ event: 'user-joined', userId: 'user-123' });
+      expect(messages[0].timestamp).toBeDefined();
+    });
+
+    it('should support event bus presenter', () => {
+      const events: Array<{ topic: string; payload: unknown; metadata: unknown }> = [];
+
+      const eventBusPresenter: UseCaseOutputPort<unknown> = {
+        present: (data: unknown) => {
+          events.push({
+            topic: 'user-events',
+            payload: data,
+            metadata: {
+              source: 'use-case',
+              timestamp: new Date().toISOString()
+            }
+          });
+        }
+      };
+
+      eventBusPresenter.present({ userId: 'user-123', action: 'created' });
+
+      expect(events).toHaveLength(1);
+      expect(events[0].topic).toBe('user-events');
+      expect(events[0].payload).toEqual({ userId: 'user-123', action: 'created' });
+      expect(events[0].metadata).toMatchObject({ source: 'use-case' });
+    });
+
+    it('should support batch presenter', () => {
+      const batches: Array<{ items: unknown[]; batchSize: number; processedAt: string }> = [];
+      let currentBatch: unknown[] = [];
+      const batchSize = 3;
+
+      const batchPresenter: UseCaseOutputPort<unknown> = {
+        present: (data: unknown) => {
+          currentBatch.push(data);
+
+          if (currentBatch.length >= batchSize) {
+            batches.push({
+              items: [...currentBatch],
+              batchSize: currentBatch.length,
+              processedAt: new Date().toISOString()
+            });
+            currentBatch = [];
+          }
+        }
+      };
+
+      // Present 7 items
+      for (let i = 1; i <= 7; i++) {
+        batchPresenter.present({ item: i });
+      }
+
+      // Add remaining items
+      if (currentBatch.length > 0) {
+        batches.push({
+          items: [...currentBatch],
+          batchSize: currentBatch.length,
+          processedAt: new Date().toISOString()
+        });
+      }
+
+      expect(batches).toHaveLength(3);
+      expect(batches[0].items).toHaveLength(3);
+      expect(batches[1].items).toHaveLength(3);
+      expect(batches[2].items).toHaveLength(1);
+    });
+
+    it('should support caching presenter', () => {
+      const cache = new Map<string, unknown>();
+      const cacheHits: string[] = [];
+      const cacheMisses: string[] = [];
+
+      const cachingPresenter: UseCaseOutputPort<{ key: string; data: unknown }> = {
+        present: (data: { key: string; data: unknown }) => {
+          if (cache.has(data.key)) {
+            cacheHits.push(data.key);
+          } else {
+            cacheMisses.push(data.key);
+            cache.set(data.key, data.data);
+          }
+        }
+      };
+
+      cachingPresenter.present({ key: 'user-1', data: { name: 'John' } });
+      cachingPresenter.present({ key: 'user-2', data: { name: 'Jane' } });
+      cachingPresenter.present({ key: 'user-1', data: { name: 'John Updated' } });
+
+      expect(cacheHits).toHaveLength(1);
+      expect(cacheHits[0]).toBe('user-1');
+      expect(cacheMisses).toHaveLength(2);
+      expect(cacheMisses[0]).toBe('user-1');
+      expect(cacheMisses[1]).toBe('user-2');
+      expect(cache.get('user-1')).toEqual({ name: 'John Updated' });
+    });
+  });
+});

core/shared/domain/DomainEvent.test.ts

@@ -0,0 +1,297 @@
+import { describe, it, expect } from 'vitest';
+import { DomainEvent, DomainEventPublisher, DomainEventAlias } from './DomainEvent';
+
+describe('DomainEvent', () => {
+  describe('DomainEvent interface', () => {
+    it('should have required properties', () => {
+      const event: DomainEvent<{ userId: string }> = {
+        eventType: 'USER_CREATED',
+        aggregateId: 'user-123',
+        eventData: { userId: 'user-123' },
+        occurredAt: new Date('2024-01-01T00:00:00Z')
+      };
+
+      expect(event.eventType).toBe('USER_CREATED');
+      expect(event.aggregateId).toBe('user-123');
+      expect(event.eventData).toEqual({ userId: 'user-123' });
+      expect(event.occurredAt).toEqual(new Date('2024-01-01T00:00:00Z'));
+    });
+
+    it('should support different event data types', () => {
+      const stringEvent: DomainEvent<string> = {
+        eventType: 'STRING_EVENT',
+        aggregateId: 'agg-1',
+        eventData: 'some data',
+        occurredAt: new Date()
+      };
+
+      const objectEvent: DomainEvent<{ id: number; name: string }> = {
+        eventType: 'OBJECT_EVENT',
+        aggregateId: 'agg-2',
+        eventData: { id: 1, name: 'test' },
+        occurredAt: new Date()
+      };
+
+      const arrayEvent: DomainEvent<string[]> = {
+        eventType: 'ARRAY_EVENT',
+        aggregateId: 'agg-3',
+        eventData: ['a', 'b', 'c'],
+        occurredAt: new Date()
+      };
+
+      expect(stringEvent.eventData).toBe('some data');
+      expect(objectEvent.eventData).toEqual({ id: 1, name: 'test' });
+      expect(arrayEvent.eventData).toEqual(['a', 'b', 'c']);
+    });
+
+    it('should support default unknown type', () => {
+      const event: DomainEvent = {
+        eventType: 'UNKNOWN_EVENT',
+        aggregateId: 'agg-1',
+        eventData: { any: 'data' },
+        occurredAt: new Date()
+      };
+
+      expect(event.eventType).toBe('UNKNOWN_EVENT');
+      expect(event.aggregateId).toBe('agg-1');
+    });
+
+    it('should support complex event data structures', () => {
+      interface ComplexEventData {
+        userId: string;
+        changes: {
+          field: string;
+          oldValue: unknown;
+          newValue: unknown;
+        }[];
+        metadata: {
+          source: string;
+          timestamp: string;
+        };
+      }
+
+      const event: DomainEvent<ComplexEventData> = {
+        eventType: 'USER_UPDATED',
+        aggregateId: 'user-456',
+        eventData: {
+          userId: 'user-456',
+          changes: [
+            { field: 'email', oldValue: 'old@example.com', newValue: 'new@example.com' }
+          ],
+          metadata: {
+            source: 'admin-panel',
+            timestamp: '2024-01-01T12:00:00Z'
+          }
+        },
+        occurredAt: new Date('2024-01-01T12:00:00Z')
+      };
+
+      expect(event.eventData.userId).toBe('user-456');
+      expect(event.eventData.changes).toHaveLength(1);
+      expect(event.eventData.metadata.source).toBe('admin-panel');
+    });
+  });
+
+  describe('DomainEventPublisher interface', () => {
+    it('should have publish method', async () => {
+      const mockPublisher: DomainEventPublisher = {
+        publish: async (event: DomainEvent) => {
+          // Mock implementation
+          return Promise.resolve();
+        }
+      };
+
+      const event: DomainEvent<{ message: string }> = {
+        eventType: 'TEST_EVENT',
+        aggregateId: 'test-1',
+        eventData: { message: 'test' },
+        occurredAt: new Date()
+      };
+
+      // Should not throw
+      await expect(mockPublisher.publish(event)).resolves.toBeUndefined();
+    });
+
+    it('should support async publish operations', async () => {
+      const publishedEvents: DomainEvent[] = [];
+
+      const mockPublisher: DomainEventPublisher = {
+        publish: async (event: DomainEvent) => {
+          publishedEvents.push(event);
+          // Simulate async operation
+          await new Promise(resolve => setTimeout(resolve, 10));
+          return Promise.resolve();
+        }
+      };
+
+      const event1: DomainEvent = {
+        eventType: 'EVENT_1',
+        aggregateId: 'agg-1',
+        eventData: { data: 'value1' },
+        occurredAt: new Date()
+      };
+
+      const event2: DomainEvent = {
+        eventType: 'EVENT_2',
+        aggregateId: 'agg-2',
+        eventData: { data: 'value2' },
+        occurredAt: new Date()
+      };
+
+      await mockPublisher.publish(event1);
+      await mockPublisher.publish(event2);
+
+      expect(publishedEvents).toHaveLength(2);
+      expect(publishedEvents[0].eventType).toBe('EVENT_1');
+      expect(publishedEvents[1].eventType).toBe('EVENT_2');
+    });
+  });
+
+  describe('DomainEvent behavior', () => {
+    it('should support event ordering by occurredAt', () => {
+      const events: DomainEvent[] = [
+        {
+          eventType: 'EVENT_3',
+          aggregateId: 'agg-3',
+          eventData: {},
+          occurredAt: new Date('2024-01-03T00:00:00Z')
+        },
+        {
+          eventType: 'EVENT_1',
+          aggregateId: 'agg-1',
+          eventData: {},
+          occurredAt: new Date('2024-01-01T00:00:00Z')
+        },
+        {
+          eventType: 'EVENT_2',
+          aggregateId: 'agg-2',
+          eventData: {},
+          occurredAt: new Date('2024-01-02T00:00:00Z')
+        }
+      ];
+
+      const sorted = [...events].sort((a, b) => 
+        a.occurredAt.getTime() - b.occurredAt.getTime()
+      );
+
+      expect(sorted[0].eventType).toBe('EVENT_1');
+      expect(sorted[1].eventType).toBe('EVENT_2');
+      expect(sorted[2].eventType).toBe('EVENT_3');
+    });
+
+    it('should support filtering events by aggregateId', () => {
+      const events: DomainEvent[] = [
+        { eventType: 'EVENT_1', aggregateId: 'user-1', eventData: {}, occurredAt: new Date() },
+        { eventType: 'EVENT_2', aggregateId: 'user-2', eventData: {}, occurredAt: new Date() },
+        { eventType: 'EVENT_3', aggregateId: 'user-1', eventData: {}, occurredAt: new Date() }
+      ];
+
+      const user1Events = events.filter(e => e.aggregateId === 'user-1');
+      expect(user1Events).toHaveLength(2);
+      expect(user1Events[0].eventType).toBe('EVENT_1');
+      expect(user1Events[1].eventType).toBe('EVENT_3');
+    });
+
+    it('should support event replay from event store', () => {
+      // Simulating event replay pattern
+      const eventStore: DomainEvent[] = [
+        {
+          eventType: 'USER_CREATED',
+          aggregateId: 'user-123',
+          eventData: { userId: 'user-123', name: 'John' },
+          occurredAt: new Date('2024-01-01T00:00:00Z')
+        },
+        {
+          eventType: 'USER_UPDATED',
+          aggregateId: 'user-123',
+          eventData: { userId: 'user-123', email: 'john@example.com' },
+          occurredAt: new Date('2024-01-02T00:00:00Z')
+        }
+      ];
+
+      // Replay events to build current state
+      let currentState: { userId: string; name?: string; email?: string } = { userId: 'user-123' };
+      
+      for (const event of eventStore) {
+        if (event.eventType === 'USER_CREATED') {
+          const data = event.eventData as { userId: string; name: string };
+          currentState.name = data.name;
+        } else if (event.eventType === 'USER_UPDATED') {
+          const data = event.eventData as { userId: string; email: string };
+          currentState.email = data.email;
+        }
+      }
+
+      expect(currentState.name).toBe('John');
+      expect(currentState.email).toBe('john@example.com');
+    });
+
+    it('should support event sourcing pattern', () => {
+      // Event sourcing: state is derived from events
+      interface AccountState {
+        balance: number;
+        transactions: number;
+      }
+
+      const events: DomainEvent[] = [
+        {
+          eventType: 'ACCOUNT_CREATED',
+          aggregateId: 'account-1',
+          eventData: { initialBalance: 100 },
+          occurredAt: new Date('2024-01-01T00:00:00Z')
+        },
+        {
+          eventType: 'DEPOSIT',
+          aggregateId: 'account-1',
+          eventData: { amount: 50 },
+          occurredAt: new Date('2024-01-02T00:00:00Z')
+        },
+        {
+          eventType: 'WITHDRAWAL',
+          aggregateId: 'account-1',
+          eventData: { amount: 30 },
+          occurredAt: new Date('2024-01-03T00:00:00Z')
+        }
+      ];
+
+      const state: AccountState = {
+        balance: 0,
+        transactions: 0
+      };
+
+      for (const event of events) {
+        switch (event.eventType) {
+          case 'ACCOUNT_CREATED':
+            state.balance = (event.eventData as { initialBalance: number }).initialBalance;
+            state.transactions = 1;
+            break;
+          case 'DEPOSIT':
+            state.balance += (event.eventData as { amount: number }).amount;
+            state.transactions += 1;
+            break;
+          case 'WITHDRAWAL':
+            state.balance -= (event.eventData as { amount: number }).amount;
+            state.transactions += 1;
+            break;
+        }
+      }
+
+      expect(state.balance).toBe(120); // 100 + 50 - 30
+      expect(state.transactions).toBe(3);
+    });
+  });
+
+  describe('DomainEventAlias type', () => {
+    it('should be assignable to DomainEvent', () => {
+      const alias: DomainEventAlias<{ id: string }> = {
+        eventType: 'TEST',
+        aggregateId: 'agg-1',
+        eventData: { id: 'test' },
+        occurredAt: new Date()
+      };
+
+      expect(alias.eventType).toBe('TEST');
+      expect(alias.aggregateId).toBe('agg-1');
+    });
+  });
+});

core/shared/domain/Logger.test.ts

@@ -0,0 +1,372 @@
+import { describe, it, expect } from 'vitest';
+import { Logger } from './Logger';
+
+describe('Logger', () => {
+  describe('Logger interface', () => {
+    it('should have debug method', () => {
+      const logs: Array<{ message: string; context?: unknown }> = [];
+
+      const logger: Logger = {
+        debug: (message: string, context?: unknown) => {
+          logs.push({ message, context });
+        },
+        info: () => {},
+        warn: () => {},
+        error: () => {}
+      };
+
+      logger.debug('Debug message', { userId: 123 });
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].message).toBe('Debug message');
+      expect(logs[0].context).toEqual({ userId: 123 });
+    });
+
+    it('should have info method', () => {
+      const logs: Array<{ message: string; context?: unknown }> = [];
+
+      const logger: Logger = {
+        debug: () => {},
+        info: (message: string, context?: unknown) => {
+          logs.push({ message, context });
+        },
+        warn: () => {},
+        error: () => {}
+      };
+
+      logger.info('Info message', { action: 'login' });
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].message).toBe('Info message');
+      expect(logs[0].context).toEqual({ action: 'login' });
+    });
+
+    it('should have warn method', () => {
+      const logs: Array<{ message: string; context?: unknown }> = [];
+
+      const logger: Logger = {
+        debug: () => {},
+        info: () => {},
+        warn: (message: string, context?: unknown) => {
+          logs.push({ message, context });
+        },
+        error: () => {}
+      };
+
+      logger.warn('Warning message', { threshold: 0.8 });
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].message).toBe('Warning message');
+      expect(logs[0].context).toEqual({ threshold: 0.8 });
+    });
+
+    it('should have error method', () => {
+      const logs: Array<{ message: string; error?: Error; context?: unknown }> = [];
+
+      const logger: Logger = {
+        debug: () => {},
+        info: () => {},
+        warn: () => {},
+        error: (message: string, error?: Error, context?: unknown) => {
+          logs.push({ message, error, context });
+        }
+      };
+
+      const testError = new Error('Test error');
+      logger.error('Error occurred', testError, { userId: 456 });
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].message).toBe('Error occurred');
+      expect(logs[0].error).toBe(testError);
+      expect(logs[0].context).toEqual({ userId: 456 });
+    });
+
+    it('should support logging without context', () => {
+      const logs: string[] = [];
+
+      const logger: Logger = {
+        debug: (message) => logs.push(`DEBUG: ${message}`),
+        info: (message) => logs.push(`INFO: ${message}`),
+        warn: (message) => logs.push(`WARN: ${message}`),
+        error: (message) => logs.push(`ERROR: ${message}`)
+      };
+
+      logger.debug('Debug without context');
+      logger.info('Info without context');
+      logger.warn('Warn without context');
+      logger.error('Error without context');
+
+      expect(logs).toHaveLength(4);
+      expect(logs[0]).toBe('DEBUG: Debug without context');
+      expect(logs[1]).toBe('INFO: Info without context');
+      expect(logs[2]).toBe('WARN: Warn without context');
+      expect(logs[3]).toBe('ERROR: Error without context');
+    });
+  });
+
+  describe('Logger behavior', () => {
+    it('should support structured logging', () => {
+      const logs: Array<{ level: string; message: string; timestamp: string; data: unknown }> = [];
+
+      const logger: Logger = {
+        debug: (message, context) => {
+          logs.push({ level: 'debug', message, timestamp: new Date().toISOString(), data: context });
+        },
+        info: (message, context) => {
+          logs.push({ level: 'info', message, timestamp: new Date().toISOString(), data: context });
+        },
+        warn: (message, context) => {
+          logs.push({ level: 'warn', message, timestamp: new Date().toISOString(), data: context });
+        },
+        error: (message, error, context) => {
+          const data: Record<string, unknown> = { error };
+          if (context) {
+            Object.assign(data, context);
+          }
+          logs.push({ level: 'error', message, timestamp: new Date().toISOString(), data });
+        }
+      };
+
+      logger.info('User logged in', { userId: 'user-123', ip: '192.168.1.1' });
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].level).toBe('info');
+      expect(logs[0].message).toBe('User logged in');
+      expect(logs[0].data).toEqual({ userId: 'user-123', ip: '192.168.1.1' });
+    });
+
+    it('should support log level filtering', () => {
+      const logs: string[] = [];
+
+      const logger: Logger = {
+        debug: (message) => logs.push(`[DEBUG] ${message}`),
+        info: (message) => logs.push(`[INFO] ${message}`),
+        warn: (message) => logs.push(`[WARN] ${message}`),
+        error: (message) => logs.push(`[ERROR] ${message}`)
+      };
+
+      // Simulate different log levels
+      logger.debug('This is a debug message');
+      logger.info('This is an info message');
+      logger.warn('This is a warning message');
+      logger.error('This is an error message');
+
+      expect(logs).toHaveLength(4);
+      expect(logs[0]).toContain('[DEBUG]');
+      expect(logs[1]).toContain('[INFO]');
+      expect(logs[2]).toContain('[WARN]');
+      expect(logs[3]).toContain('[ERROR]');
+    });
+
+    it('should support error logging with stack trace', () => {
+      const logs: Array<{ message: string; error: Error; context?: unknown }> = [];
+
+      const logger: Logger = {
+        debug: () => {},
+        info: () => {},
+        warn: () => {},
+        error: (message: string, error?: Error, context?: unknown) => {
+          if (error) {
+            logs.push({ message, error, context });
+          }
+        }
+      };
+
+      const error = new Error('Database connection failed');
+      logger.error('Failed to connect to database', error, { retryCount: 3 });
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].message).toBe('Failed to connect to database');
+      expect(logs[0].error.message).toBe('Database connection failed');
+      expect(logs[0].error.stack).toBeDefined();
+      expect(logs[0].context).toEqual({ retryCount: 3 });
+    });
+
+    it('should support logging complex objects', () => {
+      const logs: Array<{ message: string; context: unknown }> = [];
+
+      const logger: Logger = {
+        debug: () => {},
+        info: (message, context) => logs.push({ message, context }),
+        warn: () => {},
+        error: () => {}
+      };
+
+      const complexObject = {
+        user: {
+          id: 'user-123',
+          profile: {
+            name: 'John Doe',
+            email: 'john@example.com',
+            preferences: {
+              theme: 'dark',
+              notifications: true
+            }
+          }
+        },
+        session: {
+          id: 'session-456',
+          expiresAt: new Date('2024-12-31T23:59:59Z')
+        }
+      };
+
+      logger.info('User session data', complexObject);
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].message).toBe('User session data');
+      expect(logs[0].context).toEqual(complexObject);
+    });
+
+    it('should support logging arrays', () => {
+      const logs: Array<{ message: string; context: unknown }> = [];
+
+      const logger: Logger = {
+        debug: () => {},
+        info: (message, context) => logs.push({ message, context }),
+        warn: () => {},
+        error: () => {}
+      };
+
+      const items = [
+        { id: 1, name: 'Item 1' },
+        { id: 2, name: 'Item 2' },
+        { id: 3, name: 'Item 3' }
+      ];
+
+      logger.info('Processing items', { items, count: items.length });
+
+      expect(logs).toHaveLength(1);
+      expect(logs[0].message).toBe('Processing items');
+      expect(logs[0].context).toEqual({ items, count: 3 });
+    });
+
+    it('should support logging with null and undefined values', () => {
+      const logs: Array<{ message: string; context?: unknown }> = [];
+
+      const logger: Logger = {
+        debug: () => {},
+        info: (message, context) => logs.push({ message, context }),
+        warn: () => {},
+        error: () => {}
+      };
+
+      logger.info('Null value', null);
+      logger.info('Undefined value', undefined);
+      logger.info('Mixed values', { a: null, b: undefined, c: 'value' });
+
+      expect(logs).toHaveLength(3);
+      expect(logs[0].context).toBe(null);
+      expect(logs[1].context).toBe(undefined);
+      expect(logs[2].context).toEqual({ a: null, b: undefined, c: 'value' });
+    });
+  });
+
+  describe('Logger implementation patterns', () => {
+    it('should support console logger implementation', () => {
+      const consoleLogs: string[] = [];
+      const originalConsoleDebug = console.debug;
+      const originalConsoleInfo = console.info;
+      const originalConsoleWarn = console.warn;
+      const originalConsoleError = console.error;
+
+      // Mock console methods
+      console.debug = (...args: unknown[]) => consoleLogs.push(`DEBUG: ${args.join(' ')}`);
+      console.info = (...args: unknown[]) => consoleLogs.push(`INFO: ${args.join(' ')}`);
+      console.warn = (...args: unknown[]) => consoleLogs.push(`WARN: ${args.join(' ')}`);
+      console.error = (...args: unknown[]) => consoleLogs.push(`ERROR: ${args.join(' ')}`);
+
+      const consoleLogger: Logger = {
+        debug: (message, context) => console.debug(message, context),
+        info: (message, context) => console.info(message, context),
+        warn: (message, context) => console.warn(message, context),
+        error: (message, error, context) => console.error(message, error, context)
+      };
+
+      consoleLogger.debug('Debug message', { data: 'test' });
+      consoleLogger.info('Info message', { data: 'test' });
+      consoleLogger.warn('Warn message', { data: 'test' });
+      consoleLogger.error('Error message', new Error('Test'), { data: 'test' });
+
+      // Restore console methods
+      console.debug = originalConsoleDebug;
+      console.info = originalConsoleInfo;
+      console.warn = originalConsoleWarn;
+      console.error = originalConsoleError;
+
+      expect(consoleLogs).toHaveLength(4);
+      expect(consoleLogs[0]).toContain('DEBUG:');
+      expect(consoleLogs[1]).toContain('INFO:');
+      expect(consoleLogs[2]).toContain('WARN:');
+      expect(consoleLogs[3]).toContain('ERROR:');
+    });
+
+    it('should support file logger implementation', () => {
+      const fileLogs: Array<{ timestamp: string; level: string; message: string; data?: unknown }> = [];
+
+      const fileLogger: Logger = {
+        debug: (message, context) => {
+          fileLogs.push({ timestamp: new Date().toISOString(), level: 'DEBUG', message, data: context });
+        },
+        info: (message, context) => {
+          fileLogs.push({ timestamp: new Date().toISOString(), level: 'INFO', message, data: context });
+        },
+        warn: (message, context) => {
+          fileLogs.push({ timestamp: new Date().toISOString(), level: 'WARN', message, data: context });
+        },
+        error: (message, error, context) => {
+          const data: Record<string, unknown> = { error };
+          if (context) {
+            Object.assign(data, context);
+          }
+          fileLogs.push({ timestamp: new Date().toISOString(), level: 'ERROR', message, data });
+        }
+      };
+
+      fileLogger.info('Application started', { version: '1.0.0' });
+      fileLogger.warn('High memory usage', { usage: '85%' });
+      fileLogger.error('Database error', new Error('Connection timeout'), { retry: 3 });
+
+      expect(fileLogs).toHaveLength(3);
+      expect(fileLogs[0].level).toBe('INFO');
+      expect(fileLogs[1].level).toBe('WARN');
+      expect(fileLogs[2].level).toBe('ERROR');
+      expect(fileLogs[0].data).toEqual({ version: '1.0.0' });
+    });
+
+    it('should support remote logger implementation', async () => {
+      const remoteLogs: Array<{ level: string; message: string; context?: unknown }> = [];
+
+      const remoteLogger: Logger = {
+        debug: async (message, context) => {
+          remoteLogs.push({ level: 'debug', message, context });
+          await new Promise(resolve => setTimeout(resolve, 1));
+        },
+        info: async (message, context) => {
+          remoteLogs.push({ level: 'info', message, context });
+          await new Promise(resolve => setTimeout(resolve, 1));
+        },
+        warn: async (message, context) => {
+          remoteLogs.push({ level: 'warn', message, context });
+          await new Promise(resolve => setTimeout(resolve, 1));
+        },
+        error: async (message, error, context) => {
+          const errorContext: Record<string, unknown> = { error };
+          if (context) {
+            Object.assign(errorContext, context);
+          }
+          remoteLogs.push({ level: 'error', message, context: errorContext });
+          await new Promise(resolve => setTimeout(resolve, 1));
+        }
+      };
+
+      await remoteLogger.info('User action', { action: 'click', element: 'button' });
+      await remoteLogger.warn('Performance warning', { duration: '2000ms' });
+      await remoteLogger.error('API failure', new Error('404 Not Found'), { endpoint: '/api/users' });
+
+      expect(remoteLogs).toHaveLength(3);
+      expect(remoteLogs[0].level).toBe('info');
+      expect(remoteLogs[1].level).toBe('warn');
+      expect(remoteLogs[2].level).toBe('error');
+    });
+  });
+});

core/shared/domain/Option.test.ts

@@ -0,0 +1,120 @@
+import { describe, it, expect } from 'vitest';
+import { coalesce, present } from './Option';
+
+describe('Option', () => {
+  describe('coalesce()', () => {
+    it('should return the value when it is defined', () => {
+      expect(coalesce('defined', 'fallback')).toBe('defined');
+      expect(coalesce(42, 0)).toBe(42);
+      expect(coalesce(true, false)).toBe(true);
+    });
+
+    it('should return the fallback when value is undefined', () => {
+      expect(coalesce(undefined, 'fallback')).toBe('fallback');
+      expect(coalesce(undefined, 42)).toBe(42);
+      expect(coalesce(undefined, true)).toBe(true);
+    });
+
+    it('should return the fallback when value is null', () => {
+      expect(coalesce(null, 'fallback')).toBe('fallback');
+      expect(coalesce(null, 42)).toBe(42);
+      expect(coalesce(null, true)).toBe(true);
+    });
+
+    it('should handle complex fallback values', () => {
+      const fallback = { id: 0, name: 'default' };
+      expect(coalesce(undefined, fallback)).toEqual(fallback);
+      expect(coalesce(null, fallback)).toEqual(fallback);
+      expect(coalesce({ id: 1, name: 'actual' }, fallback)).toEqual({ id: 1, name: 'actual' });
+    });
+
+    it('should handle array values', () => {
+      const fallback = [1, 2, 3];
+      expect(coalesce(undefined, fallback)).toEqual([1, 2, 3]);
+      expect(coalesce([4, 5], fallback)).toEqual([4, 5]);
+    });
+
+    it('should handle zero and empty string as valid values', () => {
+      expect(coalesce(0, 999)).toBe(0);
+      expect(coalesce('', 'fallback')).toBe('');
+      expect(coalesce(false, true)).toBe(false);
+    });
+  });
+
+  describe('present()', () => {
+    it('should return the value when it is defined and not null', () => {
+      expect(present('value')).toBe('value');
+      expect(present(42)).toBe(42);
+      expect(present(true)).toBe(true);
+      expect(present({})).toEqual({});
+      expect(present([])).toEqual([]);
+    });
+
+    it('should return undefined when value is undefined', () => {
+      expect(present(undefined)).toBe(undefined);
+    });
+
+    it('should return undefined when value is null', () => {
+      expect(present(null)).toBe(undefined);
+    });
+
+    it('should handle zero and empty string as valid values', () => {
+      expect(present(0)).toBe(0);
+      expect(present('')).toBe('');
+      expect(present(false)).toBe(false);
+    });
+
+    it('should handle complex objects', () => {
+      const obj = { id: 1, name: 'test', nested: { value: 'data' } };
+      expect(present(obj)).toEqual(obj);
+    });
+
+    it('should handle arrays', () => {
+      const arr = [1, 2, 3, 'test'];
+      expect(present(arr)).toEqual(arr);
+    });
+  });
+
+  describe('Option behavior', () => {
+    it('should work together for optional value handling', () => {
+      // Example: providing a default when value might be missing
+      const maybeValue: string | undefined = undefined;
+      const result = coalesce(maybeValue, 'default');
+      expect(result).toBe('default');
+
+      // Example: filtering out null/undefined
+      const values: (string | null | undefined)[] = ['a', null, 'b', undefined, 'c'];
+      const filtered = values.map(present).filter((v): v is string => v !== undefined);
+      expect(filtered).toEqual(['a', 'b', 'c']);
+    });
+
+    it('should support conditional value assignment', () => {
+      const config: { timeout?: number } = {};
+      const timeout = coalesce(config.timeout, 5000);
+      expect(timeout).toBe(5000);
+
+      config.timeout = 3000;
+      const timeout2 = coalesce(config.timeout, 5000);
+      expect(timeout2).toBe(3000);
+    });
+
+    it('should handle nested optional properties', () => {
+      interface User {
+        profile?: {
+          name?: string;
+          email?: string;
+        };
+      }
+
+      const user1: User = {};
+      const user2: User = { profile: {} };
+      const user3: User = { profile: { name: 'John' } };
+      const user4: User = { profile: { name: 'John', email: 'john@example.com' } };
+
+      expect(coalesce(user1.profile?.name, 'Anonymous')).toBe('Anonymous');
+      expect(coalesce(user2.profile?.name, 'Anonymous')).toBe('Anonymous');
+      expect(coalesce(user3.profile?.name, 'Anonymous')).toBe('John');
+      expect(coalesce(user4.profile?.name, 'Anonymous')).toBe('John');
+    });
+  });
+});

core/shared/domain/Result.test.ts

@@ -0,0 +1,370 @@
+import { describe, it, expect } from 'vitest';
+import { Result } from './Result';
+
+describe('Result', () => {
+  describe('Result.ok()', () => {
+    it('should create a success result with a value', () => {
+      const result = Result.ok('success-value');
+      
+      expect(result.isOk()).toBe(true);
+      expect(result.isErr()).toBe(false);
+      expect(result.unwrap()).toBe('success-value');
+    });
+
+    it('should create a success result with undefined value', () => {
+      const result = Result.ok(undefined);
+      
+      expect(result.isOk()).toBe(true);
+      expect(result.isErr()).toBe(false);
+      expect(result.unwrap()).toBe(undefined);
+    });
+
+    it('should create a success result with null value', () => {
+      const result = Result.ok(null);
+      
+      expect(result.isOk()).toBe(true);
+      expect(result.isErr()).toBe(false);
+      expect(result.unwrap()).toBe(null);
+    });
+
+    it('should create a success result with complex object', () => {
+      const complexValue = { id: 123, name: 'test', nested: { data: 'value' } };
+      const result = Result.ok(complexValue);
+      
+      expect(result.isOk()).toBe(true);
+      expect(result.unwrap()).toEqual(complexValue);
+    });
+
+    it('should create a success result with array', () => {
+      const arrayValue = [1, 2, 3, 'test'];
+      const result = Result.ok(arrayValue);
+      
+      expect(result.isOk()).toBe(true);
+      expect(result.unwrap()).toEqual(arrayValue);
+    });
+  });
+
+  describe('Result.err()', () => {
+    it('should create an error result with an error', () => {
+      const error = new Error('test error');
+      const result = Result.err(error);
+      
+      expect(result.isOk()).toBe(false);
+      expect(result.isErr()).toBe(true);
+      expect(result.unwrapErr()).toBe(error);
+    });
+
+    it('should create an error result with string error', () => {
+      const result = Result.err('string error');
+      
+      expect(result.isOk()).toBe(false);
+      expect(result.isErr()).toBe(true);
+      expect(result.unwrapErr()).toBe('string error');
+    });
+
+    it('should create an error result with object error', () => {
+      const error = { code: 'VALIDATION_ERROR', message: 'Invalid input' };
+      const result = Result.err(error);
+      
+      expect(result.isOk()).toBe(false);
+      expect(result.isErr()).toBe(true);
+      expect(result.unwrapErr()).toEqual(error);
+    });
+
+    it('should create an error result with custom error type', () => {
+      interface CustomError {
+        code: string;
+        details: Record<string, unknown>;
+      }
+
+      const error: CustomError = {
+        code: 'NOT_FOUND',
+        details: { id: '123' }
+      };
+
+      const result = Result.err<unknown, CustomError>(error);
+      
+      expect(result.isOk()).toBe(false);
+      expect(result.isErr()).toBe(true);
+      expect(result.unwrapErr()).toEqual(error);
+    });
+  });
+
+  describe('Result.isOk()', () => {
+    it('should return true for success results', () => {
+      const result = Result.ok('value');
+      expect(result.isOk()).toBe(true);
+    });
+
+    it('should return false for error results', () => {
+      const result = Result.err(new Error('error'));
+      expect(result.isOk()).toBe(false);
+    });
+  });
+
+  describe('Result.isErr()', () => {
+    it('should return false for success results', () => {
+      const result = Result.ok('value');
+      expect(result.isErr()).toBe(false);
+    });
+
+    it('should return true for error results', () => {
+      const result = Result.err(new Error('error'));
+      expect(result.isErr()).toBe(true);
+    });
+  });
+
+  describe('Result.unwrap()', () => {
+    it('should return the value for success results', () => {
+      const result = Result.ok('test-value');
+      expect(result.unwrap()).toBe('test-value');
+    });
+
+    it('should throw error for error results', () => {
+      const result = Result.err(new Error('test error'));
+      expect(() => result.unwrap()).toThrow('Called unwrap on an error result');
+    });
+
+    it('should return complex values for success results', () => {
+      const complexValue = { id: 123, data: { nested: 'value' } };
+      const result = Result.ok(complexValue);
+      expect(result.unwrap()).toEqual(complexValue);
+    });
+
+    it('should return arrays for success results', () => {
+      const arrayValue = [1, 2, 3];
+      const result = Result.ok(arrayValue);
+      expect(result.unwrap()).toEqual(arrayValue);
+    });
+  });
+
+  describe('Result.unwrapOr()', () => {
+    it('should return the value for success results', () => {
+      const result = Result.ok('actual-value');
+      expect(result.unwrapOr('default-value')).toBe('actual-value');
+    });
+
+    it('should return default value for error results', () => {
+      const result = Result.err(new Error('error'));
+      expect(result.unwrapOr('default-value')).toBe('default-value');
+    });
+
+    it('should return default value when value is undefined', () => {
+      const result = Result.ok(undefined);
+      expect(result.unwrapOr('default-value')).toBe(undefined);
+    });
+
+    it('should return default value when value is null', () => {
+      const result = Result.ok(null);
+      expect(result.unwrapOr('default-value')).toBe(null);
+    });
+  });
+
+  describe('Result.unwrapErr()', () => {
+    it('should return the error for error results', () => {
+      const error = new Error('test error');
+      const result = Result.err(error);
+      expect(result.unwrapErr()).toBe(error);
+    });
+
+    it('should throw error for success results', () => {
+      const result = Result.ok('value');
+      expect(() => result.unwrapErr()).toThrow('Called unwrapErr on a success result');
+    });
+
+    it('should return string errors', () => {
+      const result = Result.err('string error');
+      expect(result.unwrapErr()).toBe('string error');
+    });
+
+    it('should return object errors', () => {
+      const error = { code: 'ERROR', message: 'Something went wrong' };
+      const result = Result.err(error);
+      expect(result.unwrapErr()).toEqual(error);
+    });
+  });
+
+  describe('Result.map()', () => {
+    it('should transform success values', () => {
+      const result = Result.ok(5);
+      const mapped = result.map((x) => x * 2);
+      
+      expect(mapped.isOk()).toBe(true);
+      expect(mapped.unwrap()).toBe(10);
+    });
+
+    it('should not transform error results', () => {
+      const error = new Error('test error');
+      const result = Result.err<number, Error>(error);
+      const mapped = result.map((x) => x * 2);
+      
+      expect(mapped.isErr()).toBe(true);
+      expect(mapped.unwrapErr()).toBe(error);
+    });
+
+    it('should handle complex transformations', () => {
+      const result = Result.ok({ id: 1, name: 'test' });
+      const mapped = result.map((obj) => ({ ...obj, name: obj.name.toUpperCase() }));
+      
+      expect(mapped.isOk()).toBe(true);
+      expect(mapped.unwrap()).toEqual({ id: 1, name: 'TEST' });
+    });
+
+    it('should handle array transformations', () => {
+      const result = Result.ok([1, 2, 3]);
+      const mapped = result.map((arr) => arr.map((x) => x * 2));
+      
+      expect(mapped.isOk()).toBe(true);
+      expect(mapped.unwrap()).toEqual([2, 4, 6]);
+    });
+  });
+
+  describe('Result.mapErr()', () => {
+    it('should transform error values', () => {
+      const error = new Error('original error');
+      const result = Result.err<string, Error>(error);
+      const mapped = result.mapErr((e) => new Error(`wrapped: ${e.message}`));
+      
+      expect(mapped.isErr()).toBe(true);
+      expect(mapped.unwrapErr().message).toBe('wrapped: original error');
+    });
+
+    it('should not transform success results', () => {
+      const result = Result.ok('value');
+      const mapped = result.mapErr((e) => new Error(`wrapped: ${e.message}`));
+      
+      expect(mapped.isOk()).toBe(true);
+      expect(mapped.unwrap()).toBe('value');
+    });
+
+    it('should handle string error transformations', () => {
+      const result = Result.err('error message');
+      const mapped = result.mapErr((e) => e.toUpperCase());
+      
+      expect(mapped.isErr()).toBe(true);
+      expect(mapped.unwrapErr()).toBe('ERROR MESSAGE');
+    });
+
+    it('should handle object error transformations', () => {
+      const error = { code: 'ERROR', message: 'Something went wrong' };
+      const result = Result.err(error);
+      const mapped = result.mapErr((e) => ({ ...e, code: `WRAPPED_${e.code}` }));
+      
+      expect(mapped.isErr()).toBe(true);
+      expect(mapped.unwrapErr()).toEqual({ code: 'WRAPPED_ERROR', message: 'Something went wrong' });
+    });
+  });
+
+  describe('Result.andThen()', () => {
+    it('should chain success results', () => {
+      const result1 = Result.ok(5);
+      const result2 = result1.andThen((x) => Result.ok(x * 2));
+      
+      expect(result2.isOk()).toBe(true);
+      expect(result2.unwrap()).toBe(10);
+    });
+
+    it('should propagate errors through chain', () => {
+      const error = new Error('first error');
+      const result1 = Result.err<number, Error>(error);
+      const result2 = result1.andThen((x) => Result.ok(x * 2));
+      
+      expect(result2.isErr()).toBe(true);
+      expect(result2.unwrapErr()).toBe(error);
+    });
+
+    it('should handle error in chained function', () => {
+      const result1 = Result.ok(5);
+      const result2 = result1.andThen((x) => Result.err(new Error(`error at ${x}`)));
+      
+      expect(result2.isErr()).toBe(true);
+      expect(result2.unwrapErr().message).toBe('error at 5');
+    });
+
+    it('should support multiple chaining steps', () => {
+      const result = Result.ok(2)
+        .andThen((x) => Result.ok(x * 3))
+        .andThen((x) => Result.ok(x + 1))
+        .andThen((x) => Result.ok(x * 2));
+      
+      expect(result.isOk()).toBe(true);
+      expect(result.unwrap()).toBe(14); // ((2 * 3) + 1) * 2 = 14
+    });
+
+    it('should stop chaining on first error', () => {
+      const result = Result.ok(2)
+        .andThen((x) => Result.ok(x * 3))
+        .andThen((x) => Result.err(new Error('stopped here')))
+        .andThen((x) => Result.ok(x + 1)); // This should not execute
+      
+      expect(result.isErr()).toBe(true);
+      expect(result.unwrapErr().message).toBe('stopped here');
+    });
+  });
+
+  describe('Result.value getter', () => {
+    it('should return value for success results', () => {
+      const result = Result.ok('test-value');
+      expect(result.value).toBe('test-value');
+    });
+
+    it('should return undefined for error results', () => {
+      const result = Result.err(new Error('error'));
+      expect(result.value).toBe(undefined);
+    });
+
+    it('should return undefined for success results with undefined value', () => {
+      const result = Result.ok(undefined);
+      expect(result.value).toBe(undefined);
+    });
+  });
+
+  describe('Result.error getter', () => {
+    it('should return error for error results', () => {
+      const error = new Error('test error');
+      const result = Result.err(error);
+      expect(result.error).toBe(error);
+    });
+
+    it('should return undefined for success results', () => {
+      const result = Result.ok('value');
+      expect(result.error).toBe(undefined);
+    });
+
+    it('should return string errors', () => {
+      const result = Result.err('string error');
+      expect(result.error).toBe('string error');
+    });
+  });
+
+  describe('Result type safety', () => {
+    it('should work with custom error codes', () => {
+      type MyErrorCode = 'NOT_FOUND' | 'VALIDATION_ERROR' | 'PERMISSION_DENIED';
+      
+      const successResult = Result.ok<string, MyErrorCode>('data');
+      const errorResult = Result.err<string, MyErrorCode>('NOT_FOUND');
+      
+      expect(successResult.isOk()).toBe(true);
+      expect(errorResult.isErr()).toBe(true);
+    });
+
+    it('should work with ApplicationErrorCode pattern', () => {
+      interface ApplicationErrorCode<Code extends string, Details = unknown> {
+        code: Code;
+        details?: Details;
+      }
+
+      type MyErrorCodes = 'USER_NOT_FOUND' | 'INVALID_EMAIL';
+
+      const successResult = Result.ok<string, ApplicationErrorCode<MyErrorCodes>>('user');
+      const errorResult = Result.err<string, ApplicationErrorCode<MyErrorCodes>>({
+        code: 'USER_NOT_FOUND',
+        details: { userId: '123' }
+      });
+
+      expect(successResult.isOk()).toBe(true);
+      expect(errorResult.isErr()).toBe(true);
+      expect(errorResult.unwrapErr().code).toBe('USER_NOT_FOUND');
+    });
+  });
+});

core/shared/domain/Service.test.ts

@@ -0,0 +1,374 @@
+import { describe, it, expect } from 'vitest';
+import {
+  DomainService,
+  DomainCalculationService,
+  ResultDomainCalculationService,
+  DomainValidationService,
+  DomainFactoryService,
+  DomainServiceAlias,
+  DomainCalculationServiceAlias,
+  ResultDomainCalculationServiceAlias,
+  DomainValidationServiceAlias,
+  DomainFactoryServiceAlias
+} from './Service';
+import { Result } from './Result';
+
+describe('Service', () => {
+  describe('DomainService interface', () => {
+    it('should have optional serviceName property', () => {
+      const service: DomainService = {
+        serviceName: 'TestService'
+      };
+
+      expect(service.serviceName).toBe('TestService');
+    });
+
+    it('should work without serviceName', () => {
+      const service: DomainService = {};
+
+      expect(service.serviceName).toBeUndefined();
+    });
+
+    it('should support different service implementations', () => {
+      const service1: DomainService = { serviceName: 'Service1' };
+      const service2: DomainService = { serviceName: 'Service2' };
+      const service3: DomainService = {};
+
+      expect(service1.serviceName).toBe('Service1');
+      expect(service2.serviceName).toBe('Service2');
+      expect(service3.serviceName).toBeUndefined();
+    });
+  });
+
+  describe('DomainCalculationService interface', () => {
+    it('should have calculate method', () => {
+      const service: DomainCalculationService<number, number> = {
+        calculate: (input: number) => input * 2
+      };
+
+      expect(service.calculate(5)).toBe(10);
+    });
+
+    it('should support different input and output types', () => {
+      const stringService: DomainCalculationService<string, string> = {
+        calculate: (input: string) => input.toUpperCase()
+      };
+
+      const objectService: DomainCalculationService<{ x: number; y: number }, number> = {
+        calculate: (input) => input.x + input.y
+      };
+
+      expect(stringService.calculate('hello')).toBe('HELLO');
+      expect(objectService.calculate({ x: 3, y: 4 })).toBe(7);
+    });
+
+    it('should support complex calculations', () => {
+      interface CalculationInput {
+        values: number[];
+        operation: 'sum' | 'average' | 'max';
+      }
+
+      const calculator: DomainCalculationService<CalculationInput, number> = {
+        calculate: (input) => {
+          switch (input.operation) {
+            case 'sum':
+              return input.values.reduce((a, b) => a + b, 0);
+            case 'average':
+              return input.values.reduce((a, b) => a + b, 0) / input.values.length;
+            case 'max':
+              return Math.max(...input.values);
+          }
+        }
+      };
+
+      expect(calculator.calculate({ values: [1, 2, 3], operation: 'sum' })).toBe(6);
+      expect(calculator.calculate({ values: [1, 2, 3], operation: 'average' })).toBe(2);
+      expect(calculator.calculate({ values: [1, 2, 3], operation: 'max' })).toBe(3);
+    });
+  });
+
+  describe('ResultDomainCalculationService interface', () => {
+    it('should have calculate method returning Result', () => {
+      const service: ResultDomainCalculationService<number, number, string> = {
+        calculate: (input: number) => {
+          if (input < 0) {
+            return Result.err('Input must be non-negative');
+          }
+          return Result.ok(input * 2);
+        }
+      };
+
+      const successResult = service.calculate(5);
+      expect(successResult.isOk()).toBe(true);
+      expect(successResult.unwrap()).toBe(10);
+
+      const errorResult = service.calculate(-1);
+      expect(errorResult.isErr()).toBe(true);
+      expect(errorResult.unwrapErr()).toBe('Input must be non-negative');
+    });
+
+    it('should support validation logic', () => {
+      interface ValidationResult {
+        isValid: boolean;
+        errors: string[];
+      }
+
+      const validator: ResultDomainCalculationService<string, ValidationResult, string> = {
+        calculate: (input: string) => {
+          const errors: string[] = [];
+
+          if (input.length < 3) {
+            errors.push('Must be at least 3 characters');
+          }
+
+          if (!input.match(/^[a-zA-Z]+$/)) {
+            errors.push('Must contain only letters');
+          }
+
+          if (errors.length > 0) {
+            return Result.err(errors.join(', '));
+          }
+
+          return Result.ok({ isValid: true, errors: [] });
+        }
+      };
+
+      const validResult = validator.calculate('Hello');
+      expect(validResult.isOk()).toBe(true);
+      expect(validResult.unwrap()).toEqual({ isValid: true, errors: [] });
+
+      const invalidResult = validator.calculate('ab');
+      expect(invalidResult.isErr()).toBe(true);
+      expect(invalidResult.unwrapErr()).toBe('Must be at least 3 characters');
+    });
+
+    it('should support complex business rules', () => {
+      interface DiscountInput {
+        basePrice: number;
+        customerType: 'regular' | 'premium' | 'vip';
+        hasCoupon: boolean;
+      }
+
+      const discountCalculator: ResultDomainCalculationService<DiscountInput, number, string> = {
+        calculate: (input) => {
+          let discount = 0;
+
+          // Customer type discount
+          switch (input.customerType) {
+            case 'premium':
+              discount += 0.1;
+              break;
+            case 'vip':
+              discount += 0.2;
+              break;
+          }
+
+          // Coupon discount
+          if (input.hasCoupon) {
+            discount += 0.05;
+          }
+
+          // Validate price
+          if (input.basePrice <= 0) {
+            return Result.err('Price must be positive');
+          }
+
+          const finalPrice = input.basePrice * (1 - discount);
+          return Result.ok(finalPrice);
+        }
+      };
+
+      const vipWithCoupon = discountCalculator.calculate({
+        basePrice: 100,
+        customerType: 'vip',
+        hasCoupon: true
+      });
+
+      expect(vipWithCoupon.isOk()).toBe(true);
+      expect(vipWithCoupon.unwrap()).toBe(75); // 100 * (1 - 0.2 - 0.05) = 75
+
+      const invalidPrice = discountCalculator.calculate({
+        basePrice: 0,
+        customerType: 'regular',
+        hasCoupon: false
+      });
+
+      expect(invalidPrice.isErr()).toBe(true);
+      expect(invalidPrice.unwrapErr()).toBe('Price must be positive');
+    });
+  });
+
+  describe('DomainValidationService interface', () => {
+    it('should have validate method returning Result', () => {
+      const service: DomainValidationService<string, boolean, string> = {
+        validate: (input: string) => {
+          if (input.length === 0) {
+            return Result.err('Input cannot be empty');
+          }
+          return Result.ok(true);
+        }
+      };
+
+      const validResult = service.validate('test');
+      expect(validResult.isOk()).toBe(true);
+      expect(validResult.unwrap()).toBe(true);
+
+      const invalidResult = service.validate('');
+      expect(invalidResult.isErr()).toBe(true);
+      expect(invalidResult.unwrapErr()).toBe('Input cannot be empty');
+    });
+
+    it('should support validation of complex objects', () => {
+      interface UserInput {
+        email: string;
+        password: string;
+        age: number;
+      }
+
+      const userValidator: DomainValidationService<UserInput, UserInput, string> = {
+        validate: (input) => {
+          const errors: string[] = [];
+
+          if (!input.email.includes('@')) {
+            errors.push('Invalid email format');
+          }
+
+          if (input.password.length < 8) {
+            errors.push('Password must be at least 8 characters');
+          }
+
+          if (input.age < 18) {
+            errors.push('Must be at least 18 years old');
+          }
+
+          if (errors.length > 0) {
+            return Result.err(errors.join(', '));
+          }
+
+          return Result.ok(input);
+        }
+      };
+
+      const validUser = userValidator.validate({
+        email: 'john@example.com',
+        password: 'securepassword',
+        age: 25
+      });
+
+      expect(validUser.isOk()).toBe(true);
+      expect(validUser.unwrap()).toEqual({
+        email: 'john@example.com',
+        password: 'securepassword',
+        age: 25
+      });
+
+      const invalidUser = userValidator.validate({
+        email: 'invalid-email',
+        password: 'short',
+        age: 15
+      });
+
+      expect(invalidUser.isErr()).toBe(true);
+      expect(invalidUser.unwrapErr()).toContain('Invalid email format');
+      expect(invalidUser.unwrapErr()).toContain('Password must be at least 8 characters');
+      expect(invalidUser.unwrapErr()).toContain('Must be at least 18 years old');
+    });
+  });
+
+  describe('DomainFactoryService interface', () => {
+    it('should have create method', () => {
+      const service: DomainFactoryService<string, { id: number; value: string }> = {
+        create: (input: string) => ({
+          id: input.length,
+          value: input.toUpperCase()
+        })
+      };
+
+      const result = service.create('test');
+      expect(result).toEqual({ id: 4, value: 'TEST' });
+    });
+
+    it('should support creating complex objects', () => {
+      interface CreateUserInput {
+        name: string;
+        email: string;
+      }
+
+      interface User {
+        id: string;
+        name: string;
+        email: string;
+        createdAt: Date;
+      }
+
+      const userFactory: DomainFactoryService<CreateUserInput, User> = {
+        create: (input) => ({
+          id: `user-${Date.now()}`,
+          name: input.name,
+          email: input.email,
+          createdAt: new Date()
+        })
+      };
+
+      const user = userFactory.create({
+        name: 'John Doe',
+        email: 'john@example.com'
+      });
+
+      expect(user.id).toMatch(/^user-\d+$/);
+      expect(user.name).toBe('John Doe');
+      expect(user.email).toBe('john@example.com');
+      expect(user.createdAt).toBeInstanceOf(Date);
+    });
+
+    it('should support creating value objects', () => {
+      interface AddressProps {
+        street: string;
+        city: string;
+        zipCode: string;
+      }
+
+      const addressFactory: DomainFactoryService<AddressProps, AddressProps> = {
+        create: (input) => ({
+          street: input.street.trim(),
+          city: input.city.trim(),
+          zipCode: input.zipCode.trim()
+        })
+      };
+
+      const address = addressFactory.create({
+        street: '  123 Main St  ',
+        city: '  New York  ',
+        zipCode: '  10001  '
+      });
+
+      expect(address.street).toBe('123 Main St');
+      expect(address.city).toBe('New York');
+      expect(address.zipCode).toBe('10001');
+    });
+  });
+
+  describe('ServiceAlias types', () => {
+    it('should be assignable to their base interfaces', () => {
+      const service1: DomainServiceAlias = { serviceName: 'Test' };
+      const service2: DomainCalculationServiceAlias<number, number> = {
+        calculate: (x) => x * 2
+      };
+      const service3: ResultDomainCalculationServiceAlias<number, number, string> = {
+        calculate: (x) => Result.ok(x * 2)
+      };
+      const service4: DomainValidationServiceAlias<string, boolean, string> = {
+        validate: (x) => Result.ok(x.length > 0)
+      };
+      const service5: DomainFactoryServiceAlias<string, string> = {
+        create: (x) => x.toUpperCase()
+      };
+
+      expect(service1.serviceName).toBe('Test');
+      expect(service2.calculate(5)).toBe(10);
+      expect(service3.calculate(5).isOk()).toBe(true);
+      expect(service4.validate('test').isOk()).toBe(true);
+      expect(service5.create('test')).toBe('TEST');
+    });
+  });
+});

core/shared/errors/ApplicationError.test.ts

@@ -0,0 +1,471 @@
+import { describe, it, expect } from 'vitest';
+import { ApplicationError, CommonApplicationErrorKind } from './ApplicationError';
+
+describe('ApplicationError', () => {
+  describe('ApplicationError interface', () => {
+    it('should have required properties', () => {
+      const error: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'user-service',
+        kind: 'not_found',
+        message: 'User not found'
+      };
+
+      expect(error.type).toBe('application');
+      expect(error.context).toBe('user-service');
+      expect(error.kind).toBe('not_found');
+      expect(error.message).toBe('User not found');
+    });
+
+    it('should support optional details', () => {
+      const error: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'payment-service',
+        kind: 'validation',
+        message: 'Invalid payment amount',
+        details: { amount: -100, minAmount: 0 }
+      };
+
+      expect(error.details).toEqual({ amount: -100, minAmount: 0 });
+    });
+
+    it('should support different error kinds', () => {
+      const notFoundError: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'user-service',
+        kind: 'not_found',
+        message: 'User not found'
+      };
+
+      const forbiddenError: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'admin-service',
+        kind: 'forbidden',
+        message: 'Access denied'
+      };
+
+      const conflictError: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'order-service',
+        kind: 'conflict',
+        message: 'Order already exists'
+      };
+
+      const validationError: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'form-service',
+        kind: 'validation',
+        message: 'Invalid input'
+      };
+
+      const unknownError: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'unknown-service',
+        kind: 'unknown',
+        message: 'Unknown error'
+      };
+
+      expect(notFoundError.kind).toBe('not_found');
+      expect(forbiddenError.kind).toBe('forbidden');
+      expect(conflictError.kind).toBe('conflict');
+      expect(validationError.kind).toBe('validation');
+      expect(unknownError.kind).toBe('unknown');
+    });
+
+    it('should support custom error kinds', () => {
+      const customError: ApplicationError<'RATE_LIMIT_EXCEEDED'> = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'api-gateway',
+        kind: 'RATE_LIMIT_EXCEEDED',
+        message: 'Rate limit exceeded',
+        details: { retryAfter: 60 }
+      };
+
+      expect(customError.kind).toBe('RATE_LIMIT_EXCEEDED');
+      expect(customError.details).toEqual({ retryAfter: 60 });
+    });
+  });
+
+  describe('CommonApplicationErrorKind type', () => {
+    it('should include standard error kinds', () => {
+      const kinds: CommonApplicationErrorKind[] = [
+        'not_found',
+        'forbidden',
+        'conflict',
+        'validation',
+        'unknown'
+      ];
+
+      kinds.forEach(kind => {
+        const error: ApplicationError = {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'test',
+          kind,
+          message: `Test ${kind} error`
+        };
+
+        expect(error.kind).toBe(kind);
+      });
+    });
+
+    it('should support string extension for custom kinds', () => {
+      const customKinds: CommonApplicationErrorKind[] = [
+        'CUSTOM_ERROR_1',
+        'CUSTOM_ERROR_2',
+        'BUSINESS_RULE_VIOLATION'
+      ];
+
+      customKinds.forEach(kind => {
+        const error: ApplicationError = {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'test',
+          kind,
+          message: `Test ${kind} error`
+        };
+
+        expect(error.kind).toBe(kind);
+      });
+    });
+  });
+
+  describe('ApplicationError behavior', () => {
+    it('should be assignable to Error interface', () => {
+      const error: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'test-service',
+        kind: 'validation',
+        message: 'Validation failed'
+      };
+
+      // ApplicationError extends Error
+      expect(error.type).toBe('application');
+      expect(error.message).toBe('Validation failed');
+    });
+
+    it('should support error inheritance pattern', () => {
+      class CustomApplicationError extends Error implements ApplicationError {
+        readonly type: 'application' = 'application';
+        readonly context: string;
+        readonly kind: string;
+        readonly details?: unknown;
+
+        constructor(context: string, kind: string, message: string, details?: unknown) {
+          super(message);
+          this.context = context;
+          this.kind = kind;
+          this.details = details;
+          this.name = 'CustomApplicationError';
+        }
+      }
+
+      const error = new CustomApplicationError(
+        'user-service',
+        'USER_NOT_FOUND',
+        'User with ID 123 not found',
+        { userId: '123' }
+      );
+
+      expect(error.type).toBe('application');
+      expect(error.context).toBe('user-service');
+      expect(error.kind).toBe('USER_NOT_FOUND');
+      expect(error.message).toBe('User with ID 123 not found');
+      expect(error.details).toEqual({ userId: '123' });
+      expect(error.name).toBe('CustomApplicationError');
+      expect(error.stack).toBeDefined();
+    });
+
+    it('should support error serialization', () => {
+      const error: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'payment-service',
+        kind: 'INSUFFICIENT_FUNDS',
+        message: 'Insufficient funds for transaction',
+        details: {
+          balance: 50,
+          required: 100,
+          currency: 'USD'
+        }
+      };
+
+      const serialized = JSON.stringify(error);
+      const parsed = JSON.parse(serialized);
+
+      expect(parsed.type).toBe('application');
+      expect(parsed.context).toBe('payment-service');
+      expect(parsed.kind).toBe('INSUFFICIENT_FUNDS');
+      expect(parsed.message).toBe('Insufficient funds for transaction');
+      expect(parsed.details).toEqual({
+        balance: 50,
+        required: 100,
+        currency: 'USD'
+      });
+    });
+
+    it('should support error deserialization', () => {
+      const serialized = JSON.stringify({
+        type: 'application',
+        context: 'auth-service',
+        kind: 'INVALID_CREDENTIALS',
+        message: 'Invalid username or password',
+        details: { attempt: 3 }
+      });
+
+      const parsed: ApplicationError = JSON.parse(serialized);
+
+      expect(parsed.type).toBe('application');
+      expect(parsed.context).toBe('auth-service');
+      expect(parsed.kind).toBe('INVALID_CREDENTIALS');
+      expect(parsed.message).toBe('Invalid username or password');
+      expect(parsed.details).toEqual({ attempt: 3 });
+    });
+
+    it('should support error comparison', () => {
+      const error1: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'user-service',
+        kind: 'not_found',
+        message: 'User not found'
+      };
+
+      const error2: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'user-service',
+        kind: 'not_found',
+        message: 'User not found'
+      };
+
+      const error3: ApplicationError = {
+        name: 'ApplicationError',
+        type: 'application',
+        context: 'order-service',
+        kind: 'not_found',
+        message: 'Order not found'
+      };
+
+      // Same kind and context
+      expect(error1.kind).toBe(error2.kind);
+      expect(error1.context).toBe(error2.context);
+
+      // Different context
+      expect(error1.context).not.toBe(error3.context);
+    });
+
+    it('should support error categorization', () => {
+      const errors: ApplicationError[] = [
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'user-service',
+          kind: 'not_found',
+          message: 'User not found'
+        },
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'admin-service',
+          kind: 'forbidden',
+          message: 'Access denied'
+        },
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'order-service',
+          kind: 'conflict',
+          message: 'Order already exists'
+        },
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'form-service',
+          kind: 'validation',
+          message: 'Invalid input'
+        }
+      ];
+
+      const notFoundErrors = errors.filter(e => e.kind === 'not_found');
+      const forbiddenErrors = errors.filter(e => e.kind === 'forbidden');
+      const conflictErrors = errors.filter(e => e.kind === 'conflict');
+      const validationErrors = errors.filter(e => e.kind === 'validation');
+
+      expect(notFoundErrors).toHaveLength(1);
+      expect(forbiddenErrors).toHaveLength(1);
+      expect(conflictErrors).toHaveLength(1);
+      expect(validationErrors).toHaveLength(1);
+    });
+
+    it('should support error aggregation by context', () => {
+      const errors: ApplicationError[] = [
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'user-service',
+          kind: 'not_found',
+          message: 'User not found'
+        },
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'user-service',
+          kind: 'validation',
+          message: 'Invalid user data'
+        },
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'order-service',
+          kind: 'not_found',
+          message: 'Order not found'
+        }
+      ];
+
+      const userErrors = errors.filter(e => e.context === 'user-service');
+      const orderErrors = errors.filter(e => e.context === 'order-service');
+
+      expect(userErrors).toHaveLength(2);
+      expect(orderErrors).toHaveLength(1);
+    });
+  });
+
+  describe('ApplicationError implementation patterns', () => {
+    it('should support error factory pattern', () => {
+      function createApplicationError<K extends string>(
+        context: string,
+        kind: K,
+        message: string,
+        details?: unknown
+      ): ApplicationError<K> {
+        return {
+          name: 'ApplicationError',
+          type: 'application',
+          context,
+          kind,
+          message,
+          details
+        };
+      }
+
+      const notFoundError = createApplicationError(
+        'user-service',
+        'USER_NOT_FOUND',
+        'User not found',
+        { userId: '123' }
+      );
+
+      const validationError = createApplicationError(
+        'form-service',
+        'VALIDATION_ERROR',
+        'Invalid form data',
+        { field: 'email', value: 'invalid' }
+      );
+
+      expect(notFoundError.kind).toBe('USER_NOT_FOUND');
+      expect(notFoundError.details).toEqual({ userId: '123' });
+      expect(validationError.kind).toBe('VALIDATION_ERROR');
+      expect(validationError.details).toEqual({ field: 'email', value: 'invalid' });
+    });
+
+    it('should support error builder pattern', () => {
+      class ApplicationErrorBuilder<K extends string> {
+        private context: string = '';
+        private kind: K = '' as K;
+        private message: string = '';
+        private details?: unknown;
+
+        withContext(context: string): this {
+          this.context = context;
+          return this;
+        }
+
+        withKind(kind: K): this {
+          this.kind = kind;
+          return this;
+        }
+
+        withMessage(message: string): this {
+          this.message = message;
+          return this;
+        }
+
+        withDetails(details: unknown): this {
+          this.details = details;
+          return this;
+        }
+
+        build(): ApplicationError<K> {
+          return {
+            name: 'ApplicationError',
+            type: 'application',
+            context: this.context,
+            kind: this.kind,
+            message: this.message,
+            details: this.details
+          };
+        }
+      }
+
+      const error = new ApplicationErrorBuilder<'USER_NOT_FOUND'>()
+        .withContext('user-service')
+        .withKind('USER_NOT_FOUND')
+        .withMessage('User not found')
+        .withDetails({ userId: '123' })
+        .build();
+
+      expect(error.type).toBe('application');
+      expect(error.context).toBe('user-service');
+      expect(error.kind).toBe('USER_NOT_FOUND');
+      expect(error.message).toBe('User not found');
+      expect(error.details).toEqual({ userId: '123' });
+    });
+
+    it('should support error categorization by severity', () => {
+      const errors: ApplicationError[] = [
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'auth-service',
+          kind: 'INVALID_CREDENTIALS',
+          message: 'Invalid credentials',
+          details: { severity: 'high' }
+        },
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'user-service',
+          kind: 'USER_NOT_FOUND',
+          message: 'User not found',
+          details: { severity: 'medium' }
+        },
+        {
+          name: 'ApplicationError',
+          type: 'application',
+          context: 'cache-service',
+          kind: 'CACHE_MISS',
+          message: 'Cache miss',
+          details: { severity: 'low' }
+        }
+      ];
+
+      const highSeverity = errors.filter(e => (e.details as { severity: string })?.severity === 'high');
+      const mediumSeverity = errors.filter(e => (e.details as { severity: string })?.severity === 'medium');
+      const lowSeverity = errors.filter(e => (e.details as { severity: string })?.severity === 'low');
+
+      expect(highSeverity).toHaveLength(1);
+      expect(mediumSeverity).toHaveLength(1);
+      expect(lowSeverity).toHaveLength(1);
+    });
+  });
+});

core/shared/errors/ApplicationErrorCode.test.ts

@@ -0,0 +1,335 @@
+import { describe, it, expect } from 'vitest';
+import { ApplicationErrorCode } from './ApplicationErrorCode';
+
+describe('ApplicationErrorCode', () => {
+  describe('ApplicationErrorCode type', () => {
+    it('should create error code with code only', () => {
+      const errorCode: ApplicationErrorCode<'USER_NOT_FOUND'> = {
+        code: 'USER_NOT_FOUND'
+      };
+
+      expect(errorCode.code).toBe('USER_NOT_FOUND');
+    });
+
+    it('should create error code with code and details', () => {
+      const errorCode: ApplicationErrorCode<'INSUFFICIENT_FUNDS', { balance: number; required: number }> = {
+        code: 'INSUFFICIENT_FUNDS',
+        details: { balance: 50, required: 100 }
+      };
+
+      expect(errorCode.code).toBe('INSUFFICIENT_FUNDS');
+      expect(errorCode.details).toEqual({ balance: 50, required: 100 });
+    });
+
+    it('should support different error code types', () => {
+      const notFoundCode: ApplicationErrorCode<'USER_NOT_FOUND'> = {
+        code: 'USER_NOT_FOUND'
+      };
+
+      const validationCode: ApplicationErrorCode<'VALIDATION_ERROR', { field: string }> = {
+        code: 'VALIDATION_ERROR',
+        details: { field: 'email' }
+      };
+
+      const permissionCode: ApplicationErrorCode<'PERMISSION_DENIED', { resource: string }> = {
+        code: 'PERMISSION_DENIED',
+        details: { resource: 'admin-panel' }
+      };
+
+      expect(notFoundCode.code).toBe('USER_NOT_FOUND');
+      expect(validationCode.code).toBe('VALIDATION_ERROR');
+      expect(validationCode.details).toEqual({ field: 'email' });
+      expect(permissionCode.code).toBe('PERMISSION_DENIED');
+      expect(permissionCode.details).toEqual({ resource: 'admin-panel' });
+    });
+
+    it('should support complex details types', () => {
+      interface PaymentErrorDetails {
+        amount: number;
+        currency: string;
+        retryAfter?: number;
+        attempts: number;
+      }
+
+      const paymentErrorCode: ApplicationErrorCode<'PAYMENT_FAILED', PaymentErrorDetails> = {
+        code: 'PAYMENT_FAILED',
+        details: {
+          amount: 100,
+          currency: 'USD',
+          retryAfter: 60,
+          attempts: 3
+        }
+      };
+
+      expect(paymentErrorCode.code).toBe('PAYMENT_FAILED');
+      expect(paymentErrorCode.details).toEqual({
+        amount: 100,
+        currency: 'USD',
+        retryAfter: 60,
+        attempts: 3
+      });
+    });
+
+    it('should support optional details', () => {
+      const errorCodeWithDetails: ApplicationErrorCode<'ERROR', { message: string }> = {
+        code: 'ERROR',
+        details: { message: 'Something went wrong' }
+      };
+
+      const errorCodeWithoutDetails: ApplicationErrorCode<'ERROR', undefined> = {
+        code: 'ERROR'
+      };
+
+      expect(errorCodeWithDetails.code).toBe('ERROR');
+      expect(errorCodeWithDetails.details).toEqual({ message: 'Something went wrong' });
+      expect(errorCodeWithoutDetails.code).toBe('ERROR');
+    });
+  });
+
+  describe('ApplicationErrorCode behavior', () => {
+    it('should be assignable to Result error type', () => {
+      // ApplicationErrorCode is designed to be used with Result type
+      // This test verifies the type compatibility
+      type MyErrorCodes = 'USER_NOT_FOUND' | 'VALIDATION_ERROR' | 'PERMISSION_DENIED';
+
+      const userNotFound: ApplicationErrorCode<'USER_NOT_FOUND'> = {
+        code: 'USER_NOT_FOUND'
+      };
+
+      const validationError: ApplicationErrorCode<'VALIDATION_ERROR', { field: string }> = {
+        code: 'VALIDATION_ERROR',
+        details: { field: 'email' }
+      };
+
+      const permissionError: ApplicationErrorCode<'PERMISSION_DENIED', { resource: string }> = {
+        code: 'PERMISSION_DENIED',
+        details: { resource: 'admin-panel' }
+      };
+
+      expect(userNotFound.code).toBe('USER_NOT_FOUND');
+      expect(validationError.code).toBe('VALIDATION_ERROR');
+      expect(validationError.details).toEqual({ field: 'email' });
+      expect(permissionError.code).toBe('PERMISSION_DENIED');
+      expect(permissionError.details).toEqual({ resource: 'admin-panel' });
+    });
+
+    it('should support error code patterns', () => {
+      // Common error code patterns
+      const notFoundPattern: ApplicationErrorCode<'NOT_FOUND', { resource: string; id?: string }> = {
+        code: 'NOT_FOUND',
+        details: { resource: 'user', id: '123' }
+      };
+
+      const conflictPattern: ApplicationErrorCode<'CONFLICT', { resource: string; existingId: string }> = {
+        code: 'CONFLICT',
+        details: { resource: 'order', existingId: '456' }
+      };
+
+      const validationPattern: ApplicationErrorCode<'VALIDATION_ERROR', { field: string; value: unknown; reason: string }> = {
+        code: 'VALIDATION_ERROR',
+        details: { field: 'email', value: 'invalid', reason: 'must contain @' }
+      };
+
+      expect(notFoundPattern.code).toBe('NOT_FOUND');
+      expect(notFoundPattern.details).toEqual({ resource: 'user', id: '123' });
+      expect(conflictPattern.code).toBe('CONFLICT');
+      expect(conflictPattern.details).toEqual({ resource: 'order', existingId: '456' });
+      expect(validationPattern.code).toBe('VALIDATION_ERROR');
+      expect(validationPattern.details).toEqual({ field: 'email', value: 'invalid', reason: 'must contain @' });
+    });
+
+    it('should support error code with metadata', () => {
+      interface ErrorMetadata {
+        timestamp: string;
+        requestId?: string;
+        userId?: string;
+        sessionId?: string;
+      }
+
+      const errorCode: ApplicationErrorCode<'AUTH_ERROR', ErrorMetadata> = {
+        code: 'AUTH_ERROR',
+        details: {
+          timestamp: new Date().toISOString(),
+          requestId: 'req-123',
+          userId: 'user-456',
+          sessionId: 'session-789'
+        }
+      };
+
+      expect(errorCode.code).toBe('AUTH_ERROR');
+      expect(errorCode.details).toBeDefined();
+      expect(errorCode.details?.timestamp).toBeDefined();
+      expect(errorCode.details?.requestId).toBe('req-123');
+    });
+
+    it('should support error code with retry information', () => {
+      interface RetryInfo {
+        retryAfter: number;
+        maxRetries: number;
+        currentAttempt: number;
+      }
+
+      const retryableError: ApplicationErrorCode<'RATE_LIMIT_EXCEEDED', RetryInfo> = {
+        code: 'RATE_LIMIT_EXCEEDED',
+        details: {
+          retryAfter: 60,
+          maxRetries: 3,
+          currentAttempt: 1
+        }
+      };
+
+      expect(retryableError.code).toBe('RATE_LIMIT_EXCEEDED');
+      expect(retryableError.details).toEqual({
+        retryAfter: 60,
+        maxRetries: 3,
+        currentAttempt: 1
+      });
+    });
+
+    it('should support error code with validation details', () => {
+      interface ValidationErrorDetails {
+        field: string;
+        value: unknown;
+        constraints: string[];
+        message: string;
+      }
+
+      const validationError: ApplicationErrorCode<'VALIDATION_ERROR', ValidationErrorDetails> = {
+        code: 'VALIDATION_ERROR',
+        details: {
+          field: 'email',
+          value: 'invalid-email',
+          constraints: ['must be a valid email', 'must not be empty'],
+          message: 'Email validation failed'
+        }
+      };
+
+      expect(validationError.code).toBe('VALIDATION_ERROR');
+      expect(validationError.details).toEqual({
+        field: 'email',
+        value: 'invalid-email',
+        constraints: ['must be a valid email', 'must not be empty'],
+        message: 'Email validation failed'
+      });
+    });
+  });
+
+  describe('ApplicationErrorCode implementation patterns', () => {
+    it('should support error code factory pattern', () => {
+      function createErrorCode<Code extends string, Details = unknown>(
+        code: Code,
+        details?: Details
+      ): ApplicationErrorCode<Code, Details> {
+        return details ? { code, details } : { code };
+      }
+
+      const notFound = createErrorCode('USER_NOT_FOUND');
+      const validation = createErrorCode('VALIDATION_ERROR', { field: 'email' });
+      const permission = createErrorCode('PERMISSION_DENIED', { resource: 'admin' });
+
+      expect(notFound.code).toBe('USER_NOT_FOUND');
+      expect(validation.code).toBe('VALIDATION_ERROR');
+      expect(validation.details).toEqual({ field: 'email' });
+      expect(permission.code).toBe('PERMISSION_DENIED');
+      expect(permission.details).toEqual({ resource: 'admin' });
+    });
+
+    it('should support error code builder pattern', () => {
+      class ErrorCodeBuilder<Code extends string, Details = unknown> {
+        private code: Code = '' as Code;
+        private details?: Details;
+
+        withCode(code: Code): this {
+          this.code = code;
+          return this;
+        }
+
+        withDetails(details: Details): this {
+          this.details = details;
+          return this;
+        }
+
+        build(): ApplicationErrorCode<Code, Details> {
+          return this.details ? { code: this.code, details: this.details } : { code: this.code };
+        }
+      }
+
+      const errorCode = new ErrorCodeBuilder<'USER_NOT_FOUND'>()
+        .withCode('USER_NOT_FOUND')
+        .build();
+
+      const errorCodeWithDetails = new ErrorCodeBuilder<'VALIDATION_ERROR', { field: string }>()
+        .withCode('VALIDATION_ERROR')
+        .withDetails({ field: 'email' })
+        .build();
+
+      expect(errorCode.code).toBe('USER_NOT_FOUND');
+      expect(errorCodeWithDetails.code).toBe('VALIDATION_ERROR');
+      expect(errorCodeWithDetails.details).toEqual({ field: 'email' });
+    });
+
+    it('should support error code categorization', () => {
+      const errorCodes: ApplicationErrorCode<string, unknown>[] = [
+        { code: 'USER_NOT_FOUND' },
+        { code: 'VALIDATION_ERROR', details: { field: 'email' } },
+        { code: 'PERMISSION_DENIED', details: { resource: 'admin' } },
+        { code: 'NETWORK_ERROR' }
+      ];
+
+      const notFoundCodes = errorCodes.filter(e => e.code === 'USER_NOT_FOUND');
+      const validationCodes = errorCodes.filter(e => e.code === 'VALIDATION_ERROR');
+      const permissionCodes = errorCodes.filter(e => e.code === 'PERMISSION_DENIED');
+      const networkCodes = errorCodes.filter(e => e.code === 'NETWORK_ERROR');
+
+      expect(notFoundCodes).toHaveLength(1);
+      expect(validationCodes).toHaveLength(1);
+      expect(permissionCodes).toHaveLength(1);
+      expect(networkCodes).toHaveLength(1);
+    });
+
+    it('should support error code with complex details', () => {
+      interface ComplexErrorDetails {
+        error: {
+          code: string;
+          message: string;
+          stack?: string;
+        };
+        context: {
+          service: string;
+          operation: string;
+          timestamp: string;
+        };
+        metadata: {
+          retryCount: number;
+          timeout: number;
+        };
+      }
+
+      const complexError: ApplicationErrorCode<'SYSTEM_ERROR', ComplexErrorDetails> = {
+        code: 'SYSTEM_ERROR',
+        details: {
+          error: {
+            code: 'E001',
+            message: 'System failure',
+            stack: 'Error stack trace...'
+          },
+          context: {
+            service: 'payment-service',
+            operation: 'processPayment',
+            timestamp: new Date().toISOString()
+          },
+          metadata: {
+            retryCount: 3,
+            timeout: 5000
+          }
+        }
+      };
+
+      expect(complexError.code).toBe('SYSTEM_ERROR');
+      expect(complexError.details).toBeDefined();
+      expect(complexError.details?.error.code).toBe('E001');
+      expect(complexError.details?.context.service).toBe('payment-service');
+      expect(complexError.details?.metadata.retryCount).toBe(3);
+    });
+  });
+});

core/shared/errors/DomainError.test.ts

@@ -0,0 +1,508 @@
+import { describe, it, expect } from 'vitest';
+import { DomainError, CommonDomainErrorKind, IDomainError, DomainErrorAlias } from './DomainError';
+
+describe('DomainError', () => {
+  describe('DomainError interface', () => {
+    it('should have required properties', () => {
+      const error: DomainError = {
+        name: 'DomainError',
+        type: 'domain',
+        context: 'user-service',
+        kind: 'validation',
+        message: 'Invalid user data'
+      };
+
+      expect(error.type).toBe('domain');
+      expect(error.context).toBe('user-service');
+      expect(error.kind).toBe('validation');
+      expect(error.message).toBe('Invalid user data');
+    });
+
+    it('should support different error kinds', () => {
+      const validationError: DomainError = {
+        name: 'DomainError',
+        type: 'domain',
+        context: 'form-service',
+        kind: 'validation',
+        message: 'Invalid input'
+      };
+
+      const invariantError: DomainError = {
+        name: 'DomainError',
+        type: 'domain',
+        context: 'order-service',
+        kind: 'invariant',
+        message: 'Order total must be positive'
+      };
+
+      const customError: DomainError = {
+        name: 'DomainError',
+        type: 'domain',
+        context: 'payment-service',
+        kind: 'BUSINESS_RULE_VIOLATION',
+        message: 'Payment exceeds limit'
+      };
+
+      expect(validationError.kind).toBe('validation');
+      expect(invariantError.kind).toBe('invariant');
+      expect(customError.kind).toBe('BUSINESS_RULE_VIOLATION');
+    });
+
+    it('should support custom error kinds', () => {
+      const customError: DomainError<'INVALID_STATE'> = {
+        name: 'DomainError',
+        type: 'domain',
+        context: 'state-machine',
+        kind: 'INVALID_STATE',
+        message: 'Cannot transition from current state'
+      };
+
+      expect(customError.kind).toBe('INVALID_STATE');
+    });
+  });
+
+  describe('CommonDomainErrorKind type', () => {
+    it('should include standard error kinds', () => {
+      const kinds: CommonDomainErrorKind[] = ['validation', 'invariant'];
+
+      kinds.forEach(kind => {
+        const error: DomainError = {
+          name: 'DomainError',
+          type: 'domain',
+          context: 'test',
+          kind,
+          message: `Test ${kind} error`
+        };
+
+        expect(error.kind).toBe(kind);
+      });
+    });
+
+    it('should support string extension for custom kinds', () => {
+      const customKinds: CommonDomainErrorKind[] = [
+        'BUSINESS_RULE_VIOLATION',
+        'DOMAIN_CONSTRAINT_VIOLATION',
+        'AGGREGATE_ROOT_VIOLATION'
+      ];
+
+      customKinds.forEach(kind => {
+        const error: DomainError = {
+          name: 'DomainError',
+          type: 'domain',
+          context: 'test',
+          kind,
+          message: `Test ${kind} error`
+        };
+
+        expect(error.kind).toBe(kind);
+      });
+    });
+  });
+
+  describe('DomainError behavior', () => {
+    it('should be assignable to Error interface', () => {
+      const error: DomainError = {
+        type: 'domain',
+        context: 'user-service',
+        kind: 'validation',
+        message: 'Validation failed'
+      };
+
+      // DomainError extends Error
+      expect(error.type).toBe('domain');
+      expect(error.message).toBe('Validation failed');
+    });
+
+    it('should support error inheritance pattern', () => {
+      class CustomDomainError extends Error implements DomainError {
+        readonly type: 'domain' = 'domain';
+        readonly context: string;
+        readonly kind: string;
+
+        constructor(context: string, kind: string, message: string) {
+          super(message);
+          this.context = context;
+          this.kind = kind;
+          this.name = 'CustomDomainError';
+        }
+      }
+
+      const error = new CustomDomainError(
+        'user-service',
+        'VALIDATION_ERROR',
+        'User email is invalid'
+      );
+
+      expect(error.type).toBe('domain');
+      expect(error.context).toBe('user-service');
+      expect(error.kind).toBe('VALIDATION_ERROR');
+      expect(error.message).toBe('User email is invalid');
+      expect(error.name).toBe('CustomDomainError');
+      expect(error.stack).toBeDefined();
+    });
+
+    it('should support error serialization', () => {
+      const error: DomainError = {
+        type: 'domain',
+        context: 'order-service',
+        kind: 'invariant',
+        message: 'Order total must be positive',
+        details: { total: -100 }
+      };
+
+      const serialized = JSON.stringify(error);
+      const parsed = JSON.parse(serialized);
+
+      expect(parsed.type).toBe('domain');
+      expect(parsed.context).toBe('order-service');
+      expect(parsed.kind).toBe('invariant');
+      expect(parsed.message).toBe('Order total must be positive');
+      expect(parsed.details).toEqual({ total: -100 });
+    });
+
+    it('should support error deserialization', () => {
+      const serialized = JSON.stringify({
+        type: 'domain',
+        context: 'payment-service',
+        kind: 'BUSINESS_RULE_VIOLATION',
+        message: 'Payment exceeds limit',
+        details: { limit: 1000, amount: 1500 }
+      });
+
+      const parsed: DomainError = JSON.parse(serialized);
+
+      expect(parsed.type).toBe('domain');
+      expect(parsed.context).toBe('payment-service');
+      expect(parsed.kind).toBe('BUSINESS_RULE_VIOLATION');
+      expect(parsed.message).toBe('Payment exceeds limit');
+      expect(parsed.details).toEqual({ limit: 1000, amount: 1500 });
+    });
+
+    it('should support error comparison', () => {
+      const error1: DomainError = {
+        type: 'domain',
+        context: 'user-service',
+        kind: 'validation',
+        message: 'Invalid email'
+      };
+
+      const error2: DomainError = {
+        type: 'domain',
+        context: 'user-service',
+        kind: 'validation',
+        message: 'Invalid email'
+      };
+
+      const error3: DomainError = {
+        type: 'domain',
+        context: 'order-service',
+        kind: 'invariant',
+        message: 'Order total must be positive'
+      };
+
+      // Same kind and context
+      expect(error1.kind).toBe(error2.kind);
+      expect(error1.context).toBe(error2.context);
+
+      // Different context
+      expect(error1.context).not.toBe(error3.context);
+    });
+
+    it('should support error categorization', () => {
+      const errors: DomainError[] = [
+        {
+          type: 'domain',
+          context: 'user-service',
+          kind: 'validation',
+          message: 'Invalid email'
+        },
+        {
+          type: 'domain',
+          context: 'order-service',
+          kind: 'invariant',
+          message: 'Order total must be positive'
+        },
+        {
+          type: 'domain',
+          context: 'payment-service',
+          kind: 'BUSINESS_RULE_VIOLATION',
+          message: 'Payment exceeds limit'
+        }
+      ];
+
+      const validationErrors = errors.filter(e => e.kind === 'validation');
+      const invariantErrors = errors.filter(e => e.kind === 'invariant');
+      const businessRuleErrors = errors.filter(e => e.kind === 'BUSINESS_RULE_VIOLATION');
+
+      expect(validationErrors).toHaveLength(1);
+      expect(invariantErrors).toHaveLength(1);
+      expect(businessRuleErrors).toHaveLength(1);
+    });
+
+    it('should support error aggregation by context', () => {
+      const errors: DomainError[] = [
+        {
+          type: 'domain',
+          context: 'user-service',
+          kind: 'validation',
+          message: 'Invalid email'
+        },
+        {
+          type: 'domain',
+          context: 'user-service',
+          kind: 'invariant',
+          message: 'User must have at least one role'
+        },
+        {
+          type: 'domain',
+          context: 'order-service',
+          kind: 'invariant',
+          message: 'Order total must be positive'
+        }
+      ];
+
+      const userErrors = errors.filter(e => e.context === 'user-service');
+      const orderErrors = errors.filter(e => e.context === 'order-service');
+
+      expect(userErrors).toHaveLength(2);
+      expect(orderErrors).toHaveLength(1);
+    });
+  });
+
+  describe('IDomainError interface', () => {
+    it('should be assignable to DomainError', () => {
+      const error: IDomainError = {
+        type: 'domain',
+        context: 'user-service',
+        kind: 'validation',
+        message: 'Invalid email'
+      };
+
+      expect(error.type).toBe('domain');
+      expect(error.context).toBe('user-service');
+      expect(error.kind).toBe('validation');
+      expect(error.message).toBe('Invalid email');
+    });
+
+    it('should support different error kinds', () => {
+      const validationError: IDomainError = {
+        type: 'domain',
+        context: 'form-service',
+        kind: 'validation',
+        message: 'Invalid input'
+      };
+
+      const invariantError: IDomainError = {
+        type: 'domain',
+        context: 'order-service',
+        kind: 'invariant',
+        message: 'Order total must be positive'
+      };
+
+      expect(validationError.kind).toBe('validation');
+      expect(invariantError.kind).toBe('invariant');
+    });
+  });
+
+  describe('DomainErrorAlias type', () => {
+    it('should be assignable to DomainError', () => {
+      const alias: DomainErrorAlias = {
+        type: 'domain',
+        context: 'user-service',
+        kind: 'validation',
+        message: 'Invalid email'
+      };
+
+      expect(alias.type).toBe('domain');
+      expect(alias.context).toBe('user-service');
+      expect(alias.kind).toBe('validation');
+      expect(alias.message).toBe('Invalid email');
+    });
+
+    it('should support different error kinds', () => {
+      const validationError: DomainErrorAlias = {
+        type: 'domain',
+        context: 'form-service',
+        kind: 'validation',
+        message: 'Invalid input'
+      };
+
+      const invariantError: DomainErrorAlias = {
+        type: 'domain',
+        context: 'order-service',
+        kind: 'invariant',
+        message: 'Order total must be positive'
+      };
+
+      expect(validationError.kind).toBe('validation');
+      expect(invariantError.kind).toBe('invariant');
+    });
+  });
+
+  describe('DomainError implementation patterns', () => {
+    it('should support error factory pattern', () => {
+      function createDomainError<K extends string>(
+        context: string,
+        kind: K,
+        message: string,
+        details?: unknown
+      ): DomainError<K> {
+        return {
+          type: 'domain',
+          context,
+          kind,
+          message,
+          details
+        };
+      }
+
+      const validationError = createDomainError(
+        'user-service',
+        'VALIDATION_ERROR',
+        'Invalid email',
+        { field: 'email', value: 'invalid' }
+      );
+
+      const invariantError = createDomainError(
+        'order-service',
+        'INVARIANT_VIOLATION',
+        'Order total must be positive'
+      );
+
+      expect(validationError.kind).toBe('VALIDATION_ERROR');
+      expect(validationError.details).toEqual({ field: 'email', value: 'invalid' });
+      expect(invariantError.kind).toBe('INVARIANT_VIOLATION');
+      expect(invariantError.details).toBeUndefined();
+    });
+
+    it('should support error builder pattern', () => {
+      class DomainErrorBuilder<K extends string> {
+        private context: string = '';
+        private kind: K = '' as K;
+        private message: string = '';
+        private details?: unknown;
+
+        withContext(context: string): this {
+          this.context = context;
+          return this;
+        }
+
+        withKind(kind: K): this {
+          this.kind = kind;
+          return this;
+        }
+
+        withMessage(message: string): this {
+          this.message = message;
+          return this;
+        }
+
+        withDetails(details: unknown): this {
+          this.details = details;
+          return this;
+        }
+
+        build(): DomainError<K> {
+          return {
+            type: 'domain',
+            context: this.context,
+            kind: this.kind,
+            message: this.message,
+            details: this.details
+          };
+        }
+      }
+
+      const error = new DomainErrorBuilder<'VALIDATION_ERROR'>()
+        .withContext('user-service')
+        .withKind('VALIDATION_ERROR')
+        .withMessage('Invalid email')
+        .withDetails({ field: 'email', value: 'invalid' })
+        .build();
+
+      expect(error.type).toBe('domain');
+      expect(error.context).toBe('user-service');
+      expect(error.kind).toBe('VALIDATION_ERROR');
+      expect(error.message).toBe('Invalid email');
+      expect(error.details).toEqual({ field: 'email', value: 'invalid' });
+    });
+
+    it('should support error categorization by severity', () => {
+      const errors: DomainError[] = [
+        {
+          type: 'domain',
+          context: 'user-service',
+          kind: 'VALIDATION_ERROR',
+          message: 'Invalid email',
+          details: { severity: 'low' }
+        },
+        {
+          type: 'domain',
+          context: 'order-service',
+          kind: 'INVARIANT_VIOLATION',
+          message: 'Order total must be positive',
+          details: { severity: 'high' }
+        },
+        {
+          type: 'domain',
+          context: 'payment-service',
+          kind: 'BUSINESS_RULE_VIOLATION',
+          message: 'Payment exceeds limit',
+          details: { severity: 'critical' }
+        }
+      ];
+
+      const lowSeverity = errors.filter(e => (e.details as { severity: string })?.severity === 'low');
+      const highSeverity = errors.filter(e => (e.details as { severity: string })?.severity === 'high');
+      const criticalSeverity = errors.filter(e => (e.details as { severity: string })?.severity === 'critical');
+
+      expect(lowSeverity).toHaveLength(1);
+      expect(highSeverity).toHaveLength(1);
+      expect(criticalSeverity).toHaveLength(1);
+    });
+
+    it('should support domain invariant violations', () => {
+      const invariantError: DomainError<'INVARIANT_VIOLATION'> = {
+        type: 'domain',
+        context: 'order-service',
+        kind: 'INVARIANT_VIOLATION',
+        message: 'Order total must be positive',
+        details: {
+          invariant: 'total > 0',
+          actualValue: -100,
+          expectedValue: '> 0'
+        }
+      };
+
+      expect(invariantError.kind).toBe('INVARIANT_VIOLATION');
+      expect(invariantError.details).toEqual({
+        invariant: 'total > 0',
+        actualValue: -100,
+        expectedValue: '> 0'
+      });
+    });
+
+    it('should support business rule violations', () => {
+      const businessRuleError: DomainError<'BUSINESS_RULE_VIOLATION'> = {
+        type: 'domain',
+        context: 'payment-service',
+        kind: 'BUSINESS_RULE_VIOLATION',
+        message: 'Payment exceeds limit',
+        details: {
+          rule: 'payment_limit',
+          limit: 1000,
+          attempted: 1500,
+          currency: 'USD'
+        }
+      };
+
+      expect(businessRuleError.kind).toBe('BUSINESS_RULE_VIOLATION');
+      expect(businessRuleError.details).toEqual({
+        rule: 'payment_limit',
+        limit: 1000,
+        attempted: 1500,
+        currency: 'USD'
+      });
+    });
+  });
+});