Testing TypeScript Services

When to use

• Adding tests for services or use-cases
• Refactoring untestable code
• Designing the test strategy for a feature

Core rules

1. Unit tests for domain entities and value objects (no mocks, pure assertions)
2. Use-cases tested with hand-rolled fakes (not jest.mock)
3. Integration tests for infrastructure adapters (real or test DB)
4. Contract tests for ports (ensure adapters satisfy interface)
5. No test logic in production code; no if (process.env.NODE_ENV === 'test')

Reference shape (TypeScript)