What is Jest?
What Jest is, why it's the default choice for testing JavaScript, and how to set it up in your project.
Unit Testing with Jest
Write your first Jest tests — test functions, handle async code, use matchers, and structure test files professionally.
Mocking in Jest
Mock modules, functions, timers, and external APIs in Jest to isolate units under test.
Async Testing
Test promises, async/await, rejections, and time-based code in Jest — fake timers, retries, and the mistakes that make async tests pass when they should fail.
Snapshot Testing
Jest snapshot testing explained — how toMatchSnapshot works, where snapshots genuinely help, and why they quietly rot into a suite nobody trusts.