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 …

Jest can be used in projects that use webpack to manage assets, styles, and compilation. webpack does offer some unique challenges over other tools. Refer to the webpack guide to get started.

Note: Jest documentation uses yarn commands, but npm will also work. You can compare yarn and npm commands in the yarn docs, here. Let's get started by writing a test for a hypothetical function that …

In your test files, Jest puts each of these methods and objects into the global environment. You don't have to require or import anything to use them. However, if you prefer explicit imports, you can do …

Jest runs the code of your project as JavaScript, hence a transformer is needed if you use some syntax not supported by Node out of the box (such as JSX, TypeScript, Vue templates).

See React: Function and Class Components. Reminders that with Class components, we expect Jest to be used to test props and not methods directly. Now let's use React's test renderer and Jest's …

Jest is a universal testing platform, with the ability to adapt to any JavaScript library or framework. In this section, we'd like to link to community posts and articles about integrating Jest into popular JS libraries.

You can cherry pick specific features of Jest and use them as standalone packages. Here's a list of the available packages:

The jest command line runner has a number of useful options. You can run jest --help to view all available options. Many of the options shown below can also be used together to run tests exactly …

The jest object is automatically in scope within every test file. The methods in the jest object help create mocks and let you control Jest's overall behavior. It can also be imported explicitly by via import from …