nestjs-testing

Unit testing NestJS modules uses TestingModule to configure providers and mocks. Create a TestingModule with your module's providers, replace real dependencies with mocks, and use Jest to verify module behavior in isolation.

Yes, mock TypeORM repositories by using getRepositoryToken to inject fake implementations into TestingModule. This allows you to test services that depend on database repositories without touching the database.

Integration testing validates controller and service interaction by configuring TestingModule with both components, mocking external dependencies, and using Jest spies and assertions to verify request handling and service calls.

Test error handling by configuring edge cases in mocked services, triggering exceptions through Jest assertions, and validating that controllers catch and properly respond to errors using TestingModule.

Unit tests use TestingModule with full mocking, integration tests combine multiple modules with selective mocking, and e2e tests exercise the full stack. Each layer requires different TestingModule provider configurations.