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/e2e/test_check_cmd.py

@@ -0,0 +1,191 @@
+"""
+Check 命令端到端测试
+
+测试 yaml2pptx.py check 命令的验证功能
+"""
+
+import pytest
+import subprocess
+import sys
+from pathlib import Path
+
+
+class TestCheckCmd:
+    """check 命令测试类"""
+
+    def run_check(self, *args):
+        """辅助函数：运行 check 命令"""
+        cmd = [sys.executable, "-m", "uv", "run", "python", "yaml2pptx.py", "check"]
+        cmd.extend(args)
+        result = subprocess.run(
+            cmd,
+            capture_output=True,
+            text=True,
+            cwd=Path(__file__).parent.parent.parent
+        )
+        return result
+
+    def test_check_valid_yaml(self, sample_yaml):
+        """测试检查有效的 YAML"""
+        result = self.run_check(str(sample_yaml))
+
+        assert result.returncode == 0
+        assert "验证" in result.stdout or "通过" in result.stdout
+
+    def test_check_invalid_yaml(self, temp_dir):
+        """测试检查无效的 YAML"""
+        # 创建包含错误的 YAML
+        yaml_content = """
+metadata:
+  size: 16:9
+
+slides:
+  - elements:
+      - type: text
+        box: [1, 1, 8, 1]
+        content: "Test"
+        font:
+          color: "red"  # 无效颜色
+"""
+        yaml_path = temp_dir / "invalid.yaml"
+        yaml_path.write_text(yaml_content)
+
+        result = self.run_check(str(yaml_path))
+
+        # 应该有错误
+        assert result.returncode != 0 or "错误" in result.stdout
+
+    def test_check_with_warnings_only(self, temp_dir):
+        """测试只有警告的 YAML（验证通过但有警告）"""
+        yaml_content = """
+metadata:
+  size: 16:9
+
+slides:
+  - elements:
+      - type: text
+        box: [8, 1, 3, 1]  # 边界超出
+        content: "Test"
+        font:
+          size: 24
+"""
+        yaml_path = temp_dir / "warning.yaml"
+        yaml_path.write_text(yaml_content)
+
+        result = self.run_check(str(yaml_path))
+
+        # 应该显示警告但返回 0
+        assert "警告" in result.stdout
+
+    def test_check_with_template(self, temp_dir, sample_template):
+        """测试检查使用模板的 YAML"""
+        yaml_content = f"""
+metadata:
+  size: 16:9
+
+slides:
+  - template: title-slide
+    vars:
+      title: "Test Title"
+"""
+        yaml_path = temp_dir / "test.yaml"
+        yaml_path.write_text(yaml_content)
+
+        result = self.run_check(str(yaml_path), "--template-dir", str(sample_template))
+
+        assert result.returncode == 0
+
+    def test_check_nonexistent_template(self, temp_dir):
+        """测试检查使用不存在模板的 YAML"""
+        yaml_content = """
+metadata:
+  size: 16:9
+
+slides:
+  - template: nonexistent
+    vars:
+      title: "Test"
+"""
+        yaml_path = temp_dir / "test.yaml"
+        yaml_path.write_text(yaml_content)
+
+        result = self.run_check(str(yaml_path), "--template-dir", str(temp_dir))
+
+        # 应该有错误（模板不存在）
+        assert result.returncode != 0
+
+    def test_check_reports_multiple_errors(self, temp_dir):
+        """测试检查报告多个错误"""
+        yaml_content = """
+metadata:
+  size: 16:9
+
+slides:
+  - elements:
+      - type: text
+        box: [1, 1, 8, 1]
+        content: "Test 1"
+        font:
+          color: "red"
+
+      - type: text
+        box: [2, 2, 8, 1]
+        content: "Test 2"
+        font:
+          color: "blue"
+"""
+        yaml_path = temp_dir / "test.yaml"
+        yaml_path.write_text(yaml_content)
+
+        result = self.run_check(str(yaml_path))
+
+        output = result.stdout + result.stderr
+        # 应该报告多个错误
+        assert "错误" in output or "2" in output
+
+    def test_check_includes_location_info(self, temp_dir):
+        """测试检查包含位置信息"""
+        yaml_content = """
+metadata:
+  size: 16:9
+
+slides:
+  - elements:
+      - type: text
+        box: [1, 1, 8, 1]
+        content: "Test"
+        font:
+          color: "red"
+"""
+        yaml_path = temp_dir / "test.yaml"
+        yaml_path.write_text(yaml_content)
+
+        result = self.run_check(str(yaml_path))
+
+        output = result.stdout + result.stderr
+        # 应该包含位置信息
+        assert "幻灯片" in output or "元素" in output
+
+    def test_check_with_missing_required_variable(self, temp_dir, sample_template):
+        """测试检查缺少必需变量的模板"""
+        yaml_content = f"""
+metadata:
+  size: 16:9
+
+slides:
+  - template: title-slide
+    vars: {{}}
+"""
+        yaml_path = temp_dir / "test.yaml"
+        yaml_path.write_text(yaml_content)
+
+        result = self.run_check(str(yaml_path), "--template-dir", str(sample_template))
+
+        # 应该有错误
+        assert result.returncode != 0
+
+    def test_check_nonexistent_file(self, temp_dir):
+        """测试检查不存在的文件"""
+        result = self.run_check(str(temp_dir / "nonexistent.yaml"))
+
+        assert result.returncode != 0