backend-testing

Use Supertest to send HTTP requests against your Express app and assert on status codes, response bodies, and database state. Wrap each test suite in describe blocks, reset the database in beforeEach, and cover both success cases like 201 and failure cases like 400, 401, and 409.

Follow the AAA pattern: Arrange inputs, Act by calling the function, and Assert on outputs. Test pure functions directly, mock external dependencies with jest.mock or unittest.mock, and cover edge cases such as boundary values and invalid inputs.

Jest with Supertest suits Node.js frameworks like Express, while Pytest with FastAPI TestClient fits Python services. Both support fixtures or setup hooks, mocking, and coverage reporting, so choose based on your application's language and framework.

No, tests must never run against a production database. Use an in-memory database like SQLite or a separate test database, and reset state with migrations in beforeEach and afterEach hooks to keep tests isolated and repeatable.

Jest hangs when open handles like database connections or servers are not closed. Fix it by destroying connections and closing servers in an afterAll hook, for example calling db.destroy() and server.close() after the suite completes.

Register or log in a test user to obtain a token, then send it in the Authorization header as a Bearer token. Assert 401 for missing tokens, 403 for invalid tokens or insufficient roles, and 200 for valid authorized requests.