Jest

Jest is a JavaScript testing framework built around simplicity. It suits teams that want to write and run unit tests without spending much time on setup.

Jest runs your test files and reports which checks pass or fail. It works out of the box on most JavaScript projects and can also be configured for custom setups. Tests run in parallel in their own processes, and Jest can measure how much of your code the tests cover.

• Runs with little or no configuration
• Snapshot tests for objects and output
• Tests run in parallel processes
• Code coverage with a single flag
• Mocks imports and functions inside tests

Jest fits developers who write tests for front-end or back-end JavaScript code. It works with projects that use Babel, TypeScript, Node, React, Angular or Vue. Small teams can start with the defaults and add options later as the project grows.

Jest is open source under the MIT licence, so it is free to use. It runs on Node.js, so the machine running your tests needs Node installed. Snapshot tests are handy, but they need a review step whenever the saved output changes on purpose.