NestJSNestJS dùng Jest và cung cấp Test.createTestingModule() để tạo test environment với DI container đầy đủ.
Unit test service: tạo mock repository với jest.fn() cho mỗi method, đăng ký trong module với { provide: getRepositoryToken(Entity), useValue: mockRepo }. Test từng method riêng lẻ, verify calls với expect(mock).toHaveBeenCalledWith(), reset mocks với jest.clearAllMocks() sau mỗi test.
E2E/Integration test: dùng Test.createTestingModule({ imports: [AppModule] }), override providers với .overrideProvider(Service).useValue(mockService), tạo app với moduleFixture.createNestApplication(), init global pipes/guards, dùng supertest để call real HTTP endpoints. Ưu tiên override service thay vì repository cho integration tests để test controller + service logic mà không cần DB thật.
NestJS uses Jest and provides Test.createTestingModule() to create a test environment with a full DI container.
Unit testing a service: create a mock repository with jest.fn() for each method, register it in the module with { provide: getRepositoryToken(Entity), useValue: mockRepo }. Test each method in isolation, verify calls with expect(mock).toHaveBeenCalledWith(), reset mocks with jest.clearAllMocks() after each test.
E2E/Integration test: use Test.createTestingModule({ imports: [AppModule] }), override providers with .overrideProvider(Service).useValue(mockService), create the app with moduleFixture.createNestApplication(), init global pipes/guards, and use supertest to call real HTTP endpoints. Prefer overriding the service rather than the repository for integration tests to test controller + service logic without a real database.