Jest · 🃏 Delightful JavaScript Testing

Jest is a delightful JavaScript Testing Framework with a focus on simplicity.
It works with projects using: Babel, TypeScript, Node, React, Angular, Vue and more!
Jest aims to work out of the box, config free, on most JavaScript projects.
Make tests which 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.
From it to expect - Jest has the entire toolkit in one place. Well documented, well maintained, well good.
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.
Generate code coverage by adding the flag --coverage. No additional setup needed. Jest can collect code coverage information from entire projects, including untested files.
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.
Tests fail—when they do, Jest provides rich context why. Here are some examples:
Jest is a JavaScript testing framework designed to ensure correctness of any JavaScript codebase. It allows you to write tests with an approachable, familiar and feature-rich API that gives you results quickly.
Jest is well-documented, requires little configuration and can be extended to match your requirements.
Jest makes testing delightful.
The Jest core team and contributors regularly speak about Jest and Delightful JavaScript Testing. Check out our talk about Building High-Quality JavaScript Tools at jsconf.eu 2017 and our talk about Jest as a Platform at ReactiveConf 2017.
Jest uses Open Collective to support developers contributing to Jest.
Join 600+ donors who sponsor Jest for $3 or more per month on opencollective.com.
A lot of people! With 100m+ million downloads in the last month, and used on over 15,000,000 public repos on GitHub.
Jest is used extensively at these companies:
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