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 …

Using Parcel Jest can be used in projects that use parcel-bundler to manage assets, styles, and compilation similar to webpack. Parcel requires zero configuration. Refer to the official docs to get …

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 …

Jun 4, 2025 · Jest is fast, but due to Jest's test isolation, slow user code often exacerbates performance issues and leads to slow test runs. When tests leave behind open handles like unclosed timers or …

At Facebook, we use Jest to test React applications.

The Jest philosophy is to work great by default, but sometimes you just need more configuration power.

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.

Jest CLI Options 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 …

If you want that, you can use ts-jest instead, or just run the TypeScript compiler tsc separately (or as part of your build process). Via ts-jest ts-jest is a TypeScript preprocessor with source map support for …

Jest Platform You can cherry pick specific features of Jest and use them as standalone packages. Here's a list of the available packages: jest-changed-files Tool for identifying modified files in a git/hg …