Delightful JavaScript Testing

Jest is a delightful JavaScript Testing Framework with a focus on simplicity. Jest aims to work out of the box, config-free, on most JavaScript projects. Make tests that keep track of large objects with ease. Snapshots live either alongside your tests or embedded inline. Tests are parallelized by running them in their own processes to maximize performance. By ensuring your tests have unique global state, Jest can reliably run tests in parallel. To make things quick, Jest runs previously failed tests first and re-organizes runs based on how long test files take. Jest uses a custom resolver for imports in your tests, making it simple to mock any object outside of your test’s scope. You can use mocked imports with the rich Mock Functions API to spy on function calls with readable test syntax.