NestJS Testing Standards

Priority: P2 (MAINTENANCE)

Unit testing, integration testing, and E2E testing patterns for NestJS applications.

1. Unit Tests: Isolated logic (Services). Mock all dependencies (jest.fn()).
2. E2E Tests: Full lifecycle (test/app.e2e-spec.ts). - Rule: Use a real Test Database (Docker). Never mock the database in E2E. - Idempotency: Mandatory cleanup. Use a transaction rollback strategy or explicit TRUNCATE in afterEach to ensure tests don't leak state.

E2E Best Practices (Pro)

• Overriding: Use .overrideProvider(AuthGuard).useValue({ canActivate: () => true }) to bypass security in functional flow tests.
• Factories: Use Factory patterns (e.g. mockUserFactory()) to generate DTOs/Entities. Avoid hardcoded JSON literals.

Tools

• Runner: Jest (swc/ts-jest).
• Mocks: jest.fn(), jest.spyOn().

Setup Pattern

// Standard Setup
const module: TestingModule = await Test.createTestingModule({
  providers: [
    UsersService,
    { provide: getRepositoryToken(User), useValue: mockRepo },
  ],
}).compile();