What are the lifecycle hooks in Jest? How to use beforeAll, afterAll, beforeEach, and afterEach?

Jest provides multiple lifecycle hooks to manage test setup and teardown:

beforeAll:

• Runs once before all tests in the current test suite
• Suitable for one-time setup, like database connections
• Example: beforeAll(() => { connectDatabase(); });

afterAll:

• Runs once after all tests in the current test suite
• Suitable for cleanup, like closing database connections
• Example: afterAll(() => { disconnectDatabase(); });

beforeEach:

• Runs before each test in the current test suite
• Suitable for per-test setup, like resetting state
• Example: beforeEach(() => { resetState(); });

afterEach:

• Runs after each test in the current test suite
• Suitable for per-test cleanup, like clearing mocks
• Example: afterEach(() => { jest.clearAllMocks(); });

Scope:

• Hooks are effective within the describe block where they're defined
• Nested describe blocks inherit parent hooks
• Hooks can be defined at multiple levels

Example:

javascript
describe('User API', () => {
  beforeAll(() => setupServer());
  afterAll(() => teardownServer());
  
  beforeEach(() => {
    jest.clearAllMocks();
  });
  
  test('should create user', () => { /* ... */ });
  test('should get user', () => { /* ... */ });
});

Best Practices:

• Use beforeEach and afterEach for test isolation
• Use beforeAll and afterAll for performance optimization
• Clean up mocks and timers in afterEach
• Keep hooks simple, avoid complex logic