Jest Testing Patterns: Effective Unit and Integration Tests

Jest dominates JavaScript testing with comprehensive features. Understanding patterns for mocking, async testing, and organization produces maintainable, effective test suites.

Test Organization

Group related tests in describe blocks. Name tests describing expected behavior. Use beforeEach for common setup. Keep tests focused on single behaviors.

• Describe blocks organize related test cases
• Test names should read as behavior specifications
• Use beforeEach/afterEach for setup and cleanup
• Keep tests independent—no dependencies between tests
• Follow AAA pattern: Arrange, Act, Assert

Mocking Strategies

Mock external dependencies isolating units. Use jest.fn() for function mocks. Mock modules with jest.mock(). Reset mocks between tests preventing state leakage.