Writing Unit Tests with Jest

beforeAll(() => {
  return initializeTestDB();
});

beforeEach(() => {
  return clearTestData();
});

afterAll(() => {
  return closeTestDB();
});

Test mocking
Test assertion
Test fixtures
Test isolation
This code demonstrates test isolation through fixtures: 1) beforeAll sets up shared test environment once, 2) beforeEach ensures clean state for each test, 3) afterAll handles proper cleanup after all tests, 4) Prevents test interdependence, 5) Ensures predictable test environment, 6) Improves test reliability, 7) Follows testing best practices, 8) Enables consistent test execution regardless of order.