typescript-testing-backend

Jest integration testing against a real PostgreSQL database uses Supertest for HTTP requests and TestDatabase isolation to ensure a clean state. This approach validates API endpoints with real database interactions instead of relying on mocks.

Mocking Prisma client in TypeScript unit tests is handled by enforcing module-boundary mocking within Jest. This isolates services and controllers from database side effects, producing fast and deterministic unit test results without hitting a real database.

Co-located __tests__ folders structure places test files directly alongside source code in the same directory. This organization keeps Jest unit and integration tests near services and controllers, simplifying test discovery and maintenance.

Yes, this backend testing approach requires Jest 29 configured with @swc/jest. This specific configuration is enforced to ensure fast TypeScript compilation and consistent test execution across unit and integration suites.

Using Supertest with a TestServer setup in Jest involves initializing an isolated HTTP server instance within the test file. Supertest then sends requests to this TestServer to validate controllers against real database endpoints.

Seeded data in backend integration tests should be used when validating read operations or complex database relationships against an isolated PostgreSQL instance. The skill provides seed data guidance to ensure consistent integration test premises.