Jest Mastery

Build reliable test suites with modern unit and integration testing patterns.

Basic

Install Jest, write test files with describe and test, use expect assertions, and run your suite.

Use Jest matchers for equality, types, exceptions, async results, and custom assertions.

Use beforeEach, afterEach, beforeAll, and afterAll for test lifecycle hooks.

Mock functions, modules, and partial implementations with jest.fn and jest.mock.

Spy on methods with jest.spyOn, track calls, and override implementations temporarily.

Test callbacks, promises, async/await, and control time with fake timers.

Generate coverage reports, set thresholds, and improve meaningful test coverage.

Capture serialized output snapshots for components, objects, and API responses.

Test React components with Jest and React Testing Library using user-centric queries.

Organize maintainable Jest suites with clear structure, isolation, and performance.

Configure Jest for native ECMAScript modules in Node and TypeScript projects.

Run Jest reliably in continuous integration with caching, sharding, and reporting.