test: add comprehensive pytest test suite

Add complete test infrastructure for yaml2pptx project with 245+ tests
covering unit, integration, and end-to-end scenarios.

Test structure:
- Unit tests: elements, template system, validators, loaders, utils
- Integration tests: presentation and rendering flows
- E2E tests: CLI commands (convert, check, preview)

Key features:
- PptxFileValidator for Level 2 PPTX validation (file structure,
  element count, content matching, position tolerance)
- Comprehensive fixtures for test data consistency
- Mock-based testing for external dependencies
- Test images generated with PIL/Pillow
- Boundary case coverage for edge scenarios

Dependencies added:
- pytest, pytest-cov, pytest-mock
- pillow (for test image generation)

Documentation updated:
- README.md: test running instructions
- README_DEV.md: test development guide

Co-authored-by: OpenSpec change: add-comprehensive-tests

tests/unit/test_validators/test_geometry.py

@@ -0,0 +1,128 @@
+"""
+几何验证器单元测试
+
+测试 GeometryValidator 的元素边界检查功能
+"""
+
+import pytest
+from validators.geometry import GeometryValidator, TOLERANCE
+from validators.result import ValidationIssue
+
+
+class TestGeometryValidator:
+    """GeometryValidator 测试类"""
+
+    def test_init(self):
+        """测试初始化"""
+        validator = GeometryValidator(10, 5.625)
+        assert validator.slide_width == 10
+        assert validator.slide_height == 5.625
+
+    def test_validate_element_within_bounds(self):
+        """测试元素在边界内"""
+        validator = GeometryValidator(10, 5.625)
+        elem = type('Element', (), {
+            'box': [1, 1, 5, 2]
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 0
+
+    def test_validate_element_right_boundary_exceeded(self):
+        """测试元素右边界超出"""
+        validator = GeometryValidator(10, 5.625)
+        elem = type('Element', (), {
+            'box': [8, 1, 3, 1]  # right = 11 > 10
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 1
+        assert issues[0].level == "WARNING"
+        assert issues[0].code == "ELEMENT_OUT_OF_BOUNDS"
+        assert "右边界" in issues[0].message
+
+    def test_validate_element_bottom_boundary_exceeded(self):
+        """测试元素下边界超出"""
+        validator = GeometryValidator(10, 5.625)
+        elem = type('Element', (), {
+            'box': [1, 5, 2, 1]  # bottom = 6 > 5.625
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 1
+        assert issues[0].level == "WARNING"
+        assert issues[0].code == "ELEMENT_OUT_OF_BOUNDS"
+        assert "下边界" in issues[0].message
+
+    def test_validate_element_completely_out_of_bounds(self):
+        """测试元素完全在页面外"""
+        validator = GeometryValidator(10, 5.625)
+        elem = type('Element', (), {
+            'box': [12, 7, 2, 1]  # 完全在页面外
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 1
+        assert issues[0].level == "WARNING"
+        assert issues[0].code == "ELEMENT_COMPLETELY_OUT_OF_BOUNDS"
+
+    def test_validate_element_within_tolerance(self):
+        """测试元素在容忍度范围内"""
+        validator = GeometryValidator(10, 5.625)
+        # 右边界 = 10.05，容忍度 0.1，应该通过
+        elem = type('Element', (), {
+            'box': [8, 1, 2.05, 1]
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 0
+
+    def test_validate_element_slightly_beyond_tolerance(self):
+        """测试元素稍微超出容忍度"""
+        validator = GeometryValidator(10, 5.625)
+        # 右边界 = 10.15，超出容忍度 0.1
+        elem = type('Element', (), {
+            'box': [8, 1, 2.15, 1]
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 1
+
+    def test_validate_table_within_bounds(self):
+        """测试表格在边界内"""
+        validator = GeometryValidator(10, 5.625)
+        elem = type('Element', (), {
+            'position': [1, 1],
+            'col_widths': [2, 2, 2]
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 0
+
+    def test_validate_table_exceeds_width(self):
+        """测试表格超出页面宽度"""
+        validator = GeometryValidator(10, 5.625)
+        elem = type('Element', (), {
+            'position': [1, 1],
+            'col_widths': [3, 3, 4]  # 总宽 10，位置 1，右边界 11
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 1
+        assert issues[0].code == "TABLE_OUT_OF_BOUNDS"
+
+    def test_validate_element_without_box(self):
+        """测试没有 box 属性的元素"""
+        validator = GeometryValidator(10, 5.625)
+        elem = type('Element', (), {})()  # 没有 box 属性
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 0
+
+    def test_validate_table_without_col_widths(self):
+        """测试没有 col_widths 的表格"""
+        validator = GeometryValidator(10, 5.625)
+        elem = type('Element', (), {
+            'position': [1, 1]
+        })()
+        issues = validator.validate_element(elem, 1, 1)
+        assert len(issues) == 0
+
+
+class TestToleranceConstant:
+    """容忍度常量测试"""
+
+    def test_tolerance_value(self):
+        """测试容忍度值为 0.1"""
+        assert TOLERANCE == 0.1