How should you handle setup and teardown in Jest?

Good teardown is about removing everything that could leak into the next test. That includes fake timers, spies, mocked modules, global properties, opened handles and rows written to a shared database. If a test needs the same fresh state on its own, it must not depend on the previous test cleaning up correctly.

let server: TestServer;

beforeAll(async () => {
  server = await startTestServer();
});

beforeEach(() => {
  jest.useFakeTimers();
});

afterEach(() => {
  jest.runOnlyPendingTimers();
  jest.useRealTimers();
  jest.restoreAllMocks();
  jest.clearAllMocks();
});

afterAll(async () => {
  await server.close();
});

What must be cleaned up

• Spies and mocked implementations with restoreAllMocks or resetAllMocks
• Fake timers back to real timers
• Globals added to globalThis or window
• Database rows or files created by the test
• Subscriptions, intervals and open network handles

setupFiles runs before the test framework is installed, so it is a good place for environment stubs. setupFilesAfterEnv runs after the framework is available, which is where expect.extend, global matchers and shared beforeEach cleanup belong. globalSetup runs in a separate process and cannot share variables with tests.