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tests/unit/core/test_generation_engine.py

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+"""Unit tests for texture generation engine control flow."""
+
+import pytest
+from unittest.mock import Mock, patch, MagicMock
+import sys
+from pathlib import Path
+
+# Add src to path for imports
+src_path = Path(__file__).parent.parent.parent.parent / "src"
+sys.path.insert(0, str(src_path))
+
+from core.generation_engine import generate_texture_image
+
+
+class TestGenerateTextureImageControlFlow:
+    """Tests for generate_texture_image() control flow and error handling."""
+
+    def test_generate_texture_image_returns_none_when_pack_fails(self):
+        """
+        Test that verifies the control flow bug: when texture generation succeeds
+        but pack() fails, the function incorrectly returns (None, None) instead
+        of returning the successfully generated image.
+        
+        This test MUST fail initially because of the missing return statement
+        after line 244 in generation_engine.py.
+        """
+        # Arrange: Create mock Blender image
+        mock_blender_img = Mock()
+        mock_blender_img.name = "TestTexture_512x512"
+        mock_blender_img.filepath_raw = ""
+        mock_blender_img.pack = Mock(side_effect=RuntimeError("Pack failed"))
+        mock_blender_img.pixels = MagicMock()
+        
+        # Mock props with valid generation settings
+        mock_props = Mock()
+        mock_props.text = "Test"
+        mock_props.font_size = 64
+        mock_props.text_color = (1.0, 1.0, 1.0, 1.0)
+        mock_props.background_transparent = False
+        mock_props.background_color = (0.0, 0.0, 0.0, 1.0)
+        mock_props.font_path = "default"
+        mock_props.use_custom_font = False
+        mock_props.custom_font_path = ""
+        mock_props.prepend_text = ""
+        mock_props.append_text = ""
+        mock_props.prepend_append_layout = 'HORIZONTAL'
+        mock_props.prepend_margin = 10
+        mock_props.append_margin = 10
+        mock_props.enable_text_fitting = False
+        mock_props.generate_normal_map = False
+        
+        # Patch bpy at module level with proper structure
+        with patch('core.generation_engine.bpy') as mock_bpy:
+            # Properly structure the bpy mock
+            mock_images = Mock()
+            mock_images.new = Mock(return_value=mock_blender_img)
+            mock_images.__contains__ = Mock(return_value=False)
+            mock_bpy.data.images = mock_images
+            
+            # Patch PIL at the import level (inside the function)
+            with patch('PIL.Image') as mock_pil:
+                mock_pil_img = Mock()
+                mock_pil_img.size = (512, 512)
+                mock_pil_img.transpose = Mock(return_value=mock_pil_img)
+                mock_pil_img.getdata = Mock(return_value=[(255, 255, 255, 255)] * (512 * 512))
+                mock_pil.new.return_value = mock_pil_img
+                mock_pil.FLIP_TOP_BOTTOM = 0
+                
+                with patch('PIL.ImageDraw') as mock_draw:
+                    mock_draw_instance = Mock()
+                    mock_draw_instance.textbbox = Mock(return_value=(0, 0, 100, 50))
+                    mock_draw_instance.text = Mock()
+                    mock_draw.Draw.return_value = mock_draw_instance
+                    
+                    with patch('PIL.ImageFont') as mock_font:
+                        mock_font.load_default.return_value = Mock()
+                        
+                        # Act: Call generate_texture_image
+                        result_img, result_normal = generate_texture_image(mock_props, 512, 512)
+        
+        # Assert: Function should return the successfully generated image,
+        # not (None, None) even if pack() fails
+        # This assertion WILL FAIL due to the control flow bug
+        assert result_img is not None, (
+            "Expected function to return the generated image despite pack() failure, "
+            "but got None. This indicates a control flow bug where the function "
+            "falls through to exception handler after successful generation."
+        )
+        assert result_img == mock_blender_img, (
+            "Expected the function to return the mock Blender image"
+        )
+
+    def test_generate_texture_image_returns_image_on_success(self):
+        """
+        Test that when both generation and pack succeed, the function returns
+        the generated image (not None).
+        
+        This test should also fail initially for the same control flow reason.
+        """
+        # Arrange: Create mock Blender image with successful pack
+        mock_blender_img = Mock()
+        mock_blender_img.name = "TestTexture_512x512"
+        mock_blender_img.filepath_raw = ""
+        mock_blender_img.pack = Mock()  # Succeeds (no exception)
+        mock_blender_img.pixels = MagicMock()
+        
+        mock_props = Mock()
+        mock_props.text = "Test"
+        mock_props.font_size = 64
+        mock_props.text_color = (1.0, 1.0, 1.0, 1.0)
+        mock_props.background_transparent = False
+        mock_props.background_color = (0.0, 0.0, 0.0, 1.0)
+        mock_props.font_path = "default"
+        mock_props.use_custom_font = False
+        mock_props.custom_font_path = ""
+        mock_props.prepend_text = ""
+        mock_props.append_text = ""
+        mock_props.prepend_append_layout = 'HORIZONTAL'
+        mock_props.prepend_margin = 10
+        mock_props.append_margin = 10
+        mock_props.enable_text_fitting = False
+        mock_props.generate_normal_map = False
+        
+        with patch('core.generation_engine.bpy') as mock_bpy:
+            # Properly structure the bpy mock
+            mock_images = Mock()
+            mock_images.new = Mock(return_value=mock_blender_img)
+            mock_images.__contains__ = Mock(return_value=False)
+            mock_bpy.data.images = mock_images
+            
+            with patch('PIL.Image') as mock_pil:
+                mock_pil_img = Mock()
+                mock_pil_img.size = (512, 512)
+                mock_pil_img.transpose = Mock(return_value=mock_pil_img)
+                mock_pil_img.getdata = Mock(return_value=[(255, 255, 255, 255)] * (512 * 512))
+                mock_pil.new.return_value = mock_pil_img
+                mock_pil.FLIP_TOP_BOTTOM = 0
+                
+                with patch('PIL.ImageDraw') as mock_draw:
+                    mock_draw_instance = Mock()
+                    mock_draw_instance.textbbox = Mock(return_value=(0, 0, 100, 50))
+                    mock_draw_instance.text = Mock()
+                    mock_draw.Draw.return_value = mock_draw_instance
+                    
+                    with patch('PIL.ImageFont') as mock_font:
+                        mock_font.load_default.return_value = Mock()
+                        
+                        # Act
+                        result_img, result_normal = generate_texture_image(mock_props, 512, 512)
+        
+        # Assert: Should return the generated image
+        assert result_img is not None, (
+            "Expected function to return generated image on success, got None"
+        )
+        assert result_img == mock_blender_img
+        assert result_normal is None  # No normal map requested