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_result.py

@@ -0,0 +1,155 @@
+"""
+验证结果数据结构单元测试
+
+测试 ValidationIssue 和 ValidationResult 类
+"""
+
+import pytest
+from validators.result import ValidationIssue, ValidationResult
+
+
+class TestValidationIssue:
+    """ValidationIssue 测试类"""
+
+    def test_create_error_issue(self):
+        """测试创建错误级别问题"""
+        issue = ValidationIssue(
+            level="ERROR",
+            message="Test error",
+            location="Slide 1",
+            code="TEST_ERROR"
+        )
+        assert issue.level == "ERROR"
+        assert issue.message == "Test error"
+        assert issue.location == "Slide 1"
+        assert issue.code == "TEST_ERROR"
+
+    def test_create_warning_issue(self):
+        """测试创建警告级别问题"""
+        issue = ValidationIssue(
+            level="WARNING",
+            message="Test warning",
+            location="",
+            code="TEST_WARNING"
+        )
+        assert issue.level == "WARNING"
+
+    def test_create_info_issue(self):
+        """测试创建提示级别问题"""
+        issue = ValidationIssue(
+            level="INFO",
+            message="Test info",
+            location="",
+            code="TEST_INFO"
+        )
+        assert issue.level == "INFO"
+
+
+class TestValidationResult:
+    """ValidationResult 测试类"""
+
+    def test_create_with_defaults(self):
+        """测试使用默认值创建"""
+        result = ValidationResult(valid=True)
+        assert result.valid is True
+        assert result.errors == []
+        assert result.warnings == []
+        assert result.infos == []
+
+    def test_create_with_issues(self):
+        """测试创建包含问题的结果"""
+        errors = [ValidationIssue("ERROR", "Error 1", "", "ERR1")]
+        warnings = [ValidationIssue("WARNING", "Warning 1", "", "WARN1")]
+        infos = [ValidationIssue("INFO", "Info 1", "", "INFO1")]
+
+        result = ValidationResult(
+            valid=False,
+            errors=errors,
+            warnings=warnings,
+            infos=infos
+        )
+        assert result.valid is False
+        assert len(result.errors) == 1
+        assert len(result.warnings) == 1
+        assert len(result.infos) == 1
+
+    def test_has_errors(self):
+        """测试 has_errors 方法"""
+        result = ValidationResult(
+            valid=True,
+            errors=[ValidationIssue("ERROR", "Error", "", "ERR")]
+        )
+        assert result.has_errors() is True
+
+    def test_has_errors_no_errors(self):
+        """测试没有错误时 has_errors 返回 False"""
+        result = ValidationResult(valid=True)
+        assert result.has_errors() is False
+
+    def test_format_output_clean(self):
+        """测试格式化输出 - 无问题"""
+        result = ValidationResult(valid=True)
+        output = result.format_output()
+        assert "验证通过" in output
+
+    def test_format_output_with_errors(self):
+        """测试格式化输出 - 包含错误"""
+        result = ValidationResult(
+            valid=False,
+            errors=[
+                ValidationIssue("ERROR", "Error 1", "Slide 1", "ERR1"),
+                ValidationIssue("ERROR", "Error 2", "Slide 2", "ERR2")
+            ]
+        )
+        output = result.format_output()
+        assert "2 个错误" in output
+        assert "Error 1" in output
+        assert "Error 2" in output
+        assert "[Slide 1]" in output
+
+    def test_format_output_with_warnings(self):
+        """测试格式化输出 - 包含警告"""
+        result = ValidationResult(
+            valid=True,
+            warnings=[
+                ValidationIssue("WARNING", "Warning 1", "Slide 1", "WARN1")
+            ]
+        )
+        output = result.format_output()
+        assert "1 个警告" in output
+        assert "Warning 1" in output
+
+    def test_format_output_with_infos(self):
+        """测试格式化输出 - 包含提示"""
+        result = ValidationResult(
+            valid=True,
+            infos=[
+                ValidationIssue("INFO", "Info 1", "", "INFO1")
+            ]
+        )
+        output = result.format_output()
+        assert "1 个提示" in output
+
+    def test_format_output_mixed_issues(self):
+        """测试格式化输出 - 混合问题"""
+        result = ValidationResult(
+            valid=False,
+            errors=[ValidationIssue("ERROR", "Error", "", "ERR")],
+            warnings=[ValidationIssue("WARNING", "Warning", "", "WARN")],
+            infos=[ValidationIssue("INFO", "Info", "", "INFO")]
+        )
+        output = result.format_output()
+        assert "1 个错误" in output
+        assert "1 个警告" in output
+        assert "1 个提示" in output
+
+    def test_format_output_issue_without_location(self):
+        """测试没有位置信息的问题"""
+        result = ValidationResult(
+            valid=False,
+            errors=[ValidationIssue("ERROR", "Error", "", "ERR")]
+        )
+        output = result.format_output()
+        assert "Error" in output
+        # 不应该有位置前缀
+        assert "[]" not in output