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👩🏻‍💻 Developer Ready: A comprehensive JavaScript testing solution. Works out of the box for most JavaScript projects.

🏃🏽 Instant Feedback: Fast, interactive watch mode only runs test files related to changed files.

📸 Snapshot Testing: Capture snapshots of large objects to simplify testing and to analyze how they change over time.

See more onjestjs.io

• Getting Started
• Running from command line
• Additional Configuration
  • Generate a basic configuration file
  • Using Babel
  • Using webpack
  • Using Vite
  • Using Parcel
  • Using Typescript
• Documentation
• Badge
• Contributing
  • Code of Conduct
  • Contributing Guide
  • Good First Issues
• Credits
  • Backers
  • Sponsors
• License
• Copyright

Install Jest usingyarn:

yarn add --dev jest

Ornpm:

npm install --save-dev jest

Note: Jest documentation usesyarn commands, butnpm will also work. You can compareyarn andnpm commands in theyarn docs, here.

Let's get started by writing a test for a hypothetical function that adds two numbers. First, create asum.js file:

functionsum(a,b){returna+b;}module.exports=sum;

Then, create a file namedsum.test.js. This will contain our actual test:

constsum=require('./sum');test('adds 1 + 2 to equal 3',()=>{expect(sum(1,2)).toBe(3);});

Add the following section to yourpackage.json:

{"scripts": {"test":"jest"  }}

Finally, runyarn test ornpm test and Jest will print this message:

PASS  ./sum.test.js✓ adds 1 + 2 to equal 3 (5ms)

You just successfully wrote your first test using Jest!

This test usedexpect andtoBe to test that two values were exactly identical. To learn about the other things that Jest can test, seeUsing Matchers.

You can run Jest directly from the CLI (if it's globally available in yourPATH, e.g. byyarn global add jest ornpm install jest --global) with a variety of useful options.

Here's how to run Jest on files matchingmy-test, usingconfig.json as a configuration file and display a native OS notification after the run:

jest my-test --notify --config=config.json

If you'd like to learn more about runningjest through the command line, take a look at theJest CLI Options page.

Based on your project, Jest will ask you a few questions and will create a basic configuration file with a short description for each option:

yarn create jest

To useBabel, install required dependencies viayarn:

yarn add --dev babel-jest @babel/core @babel/preset-env

Configure Babel to target your current version of Node by creating ababel.config.js file in the root of your project:

// babel.config.jsmodule.exports={presets:[['@babel/preset-env',{targets:{node:'current'}}]],};

The ideal configuration for Babel will depend on your project. SeeBabel's docs for more details.

// babel.config.jsmodule.exports=api=>{constisTest=api.env('test');// You can use isTest to determine what presets and plugins to use.return{// ...};};

// jest.config.jsmodule.exports={transform:{},};

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

Jest can be used in projects that usevite to serves source code over native ESM to provide some frontend tooling, vite is an opinionated tool and does offer some out-of-the box workflows. Jest is not fully supported by vite due to how theplugin system from vite works, but there is some working examples for first-class jest integration using thevite-jest, since this is not fully supported, you might as well read thelimitation of thevite-jest. Refer to thevite guide to get started.

Jest can be used in projects that useparcel-bundler to manage assets, styles, and compilation similar to webpack. Parcel requires zero configuration. Refer to the officialdocs to get started.

Jest supports TypeScript, via Babel. First, make sure you followed the instructions onusing Babel above. Next, install the@babel/preset-typescript viayarn:

yarn add --dev @babel/preset-typescript

Then add@babel/preset-typescript to the list of presets in yourbabel.config.js.

// babel.config.jsmodule.exports = {  presets: [    ['@babel/preset-env', {targets: {node: 'current'}}],+    '@babel/preset-typescript',  ],};

However, there are somecaveats to using TypeScript with Babel. Because TypeScript support in Babel is purely transpilation, Jest will not type-check your tests as they are run. If you want that, you can usets-jest instead, or just run the TypeScript compilertsc separately (or as part of your build process).

Learn more about usingJest on the official site!

• Getting Started
• Guides
• API Reference
• Configuring Jest

Show the world you're usingJest→

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Development of Jest happens in the open on GitHub, and we are grateful to the community for contributing bugfixes and improvements. Read below to learn how you can take part in improving Jest.

Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please readthe full text so that you can understand what actions will and will not be tolerated.

Read ourcontributing guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to Jest.

To help you get your feet wet and get you familiar with our contribution process, we have a list ofgood first issues that contain bugs which have a relatively limited scope. This is a great place to get started.

This project exists thanks to all the people whocontribute.

Thank you to all our backers! 🙏

Support this project by becoming a sponsor. Your logo will show up here with a link to your website.

Jest isMIT licensed.

Copyright Contributors to the Jest project.