test: add comprehensive unit tests for database, parsers, loaders, and MCP tools

- Database layer tests (32 tests):
  - node-repository.ts: 100% coverage
  - template-repository.ts: 80.31% coverage
  - database-adapter.ts: interface compliance tests

- Parser tests (99 tests):
  - node-parser.ts: 93.10% coverage
  - property-extractor.ts: 95.18% coverage
  - simple-parser.ts: 91.26% coverage
  - Fixed parser bugs for version extraction

- Loader tests (22 tests):
  - node-loader.ts: comprehensive mocking tests

- MCP tools tests (85 tests):
  - tools.ts: 100% coverage
  - tools-documentation.ts: 100% coverage
  - docs-mapper.ts: 100% coverage

Total: 943 tests passing across 32 test files
Significant progress from 2.45% to ~30% overall coverage

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/unit/database/README.md

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+# Database Layer Unit Tests
+
+This directory contains comprehensive unit tests for the database layer components of n8n-mcp.
+
+## Test Coverage
+
+### node-repository.ts - 100% Coverage ✅
+- `saveNode` method with JSON serialization
+- `getNode` method with JSON deserialization  
+- `getAITools` method
+- `safeJsonParse` private method
+- Edge cases: large JSON, boolean conversion, invalid JSON handling
+
+### template-repository.ts - 80.31% Coverage ✅
+- FTS5 initialization and fallback
+- `saveTemplate` with sanitization
+- `getTemplate` and `getTemplatesByNodes`
+- `searchTemplates` with FTS5 and LIKE fallback
+- `getTemplatesForTask` with task mapping
+- Template statistics and maintenance operations
+- Uncovered: Some error paths in FTS5 operations
+
+### database-adapter.ts - Tested via Mocks
+- Interface compliance tests
+- PreparedStatement implementation
+- Transaction support
+- FTS5 detection logic
+- Error handling patterns
+
+## Test Strategy
+
+The tests use a mock-based approach to:
+1. Isolate database operations from actual database dependencies
+2. Test business logic without requiring real SQLite/sql.js
+3. Ensure consistent test execution across environments
+4. Focus on behavior rather than implementation details
+
+## Key Test Files
+
+- `node-repository-core.test.ts` - Core NodeRepository functionality
+- `template-repository-core.test.ts` - Core TemplateRepository functionality  
+- `database-adapter-unit.test.ts` - DatabaseAdapter interface and patterns
+
+## Running Tests
+
+```bash
+# Run all database tests
+npm test -- tests/unit/database/
+
+# Run with coverage
+npm run test:coverage -- tests/unit/database/
+
+# Run specific test file
+npm test -- tests/unit/database/node-repository-core.test.ts
+```
+
+## Mock Infrastructure
+
+The tests use custom mock implementations:
+- `MockDatabaseAdapter` - Simulates database operations
+- `MockPreparedStatement` - Simulates SQL statement execution
+- Mock logger and template sanitizer for external dependencies
+
+This approach ensures tests are fast, reliable, and maintainable.