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thymikee chore: remove Node 8 references and some dead code (#9284)
* chore: remove Node 8 references and some dead code

* import async hooks normally

* bump node to 8.3 because V8 6.0 with Turbofan and better perf

* update comments in pretty-format
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.circleci chore: run tsc and linting as GH action (#9223) Nov 22, 2019
.github chore: run tsc and linting as GH action (#9223) Nov 22, 2019
.vscode fix: limit number of workers when creating haste maps in projec… (#9259) Dec 3, 2019
.yarn/releases chore: test on node 13 (#9088) Oct 29, 2019
docs chore: remove Node 8 references and some dead code (#9284) Dec 9, 2019
e2e Support custom inline snapshot matchers (#9278) Dec 8, 2019
examples Add mongo db example (#7849) Nov 22, 2019
fixtures Update Facebook copyright headers (#7589) Jan 8, 2019
packages chore: remove Node 8 references and some dead code (#9284) Dec 9, 2019
scripts chore: use chokidar for watch script (#9226) Nov 24, 2019
website Docs: fix broken anchor links (#9247) Dec 1, 2019
.azure-pipelines-steps.yml chore: move "quick-install" to npm script (#9119) Nov 1, 2019
.azure-pipelines.yml chore: add caching to azure pipelines (#8866) Aug 26, 2019
.editorconfig chore: enforce LF line endings (#8809) Aug 11, 2019
.eslintignore expect: Highlight substring differences when matcher fails, part 2 (#… Jun 13, 2019
.eslintrc.js chore(lint): enable `eslint-comments/no-unused-disable` (#9241) Nov 30, 2019
.gitignore chore: upgrade TS to 3.4.0-dev* for inceremental builds (#8149) Mar 19, 2019
.npmignore Chore: npmignore tsconfig.* files. (#8641) Jul 4, 2019
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.travis.yml chore: move "quick-install" to npm script (#9119) Nov 1, 2019
.watchmanconfig add empty .watchmanconfig (#5683) Feb 27, 2018
.yarnrc chore: upgrade yarn (#9099) Oct 26, 2019 Support custom inline snapshot matchers (#9278) Dec 8, 2019 Add missing copyright headers and code of conduct (#7221) Oct 23, 2018 Add section about alphabetical order in changelog (#9281) Dec 8, 2019
LICENSE LICENSE: Follow copyright header guidelines and delete For Jest softw… May 6, 2019 Update link to webpack docs (#9078) Oct 26, 2019
TestUtils.ts chore: remove extraGlobals from GlobalConfig (#9254) Dec 1, 2019
babel.config.js Get rid of Node 6 support (#8455) Aug 22, 2019
crowdin.yaml Upgrade prettier (#6846) Aug 15, 2018
jest set correct stack trace for async rejections of non-errors (#6230) May 23, 2018
jest-worker Add node worker-thread support to jest-worker (#7408) Dec 5, 2018 chore: remove Node 8 references and some dead code (#9284) Dec 9, 2019
jest.config.js chore: Make sure copyright header comment includes license (#8783) Aug 6, 2019
jsconfig.json Add Jest Editor Support (#2192) Dec 7, 2016
karma.conf.js Correctly bundle up for browser globals (#7661) Jan 20, 2019
lerna.json chore: update strip-ansi (#9158) Nov 10, 2019
package.json chore: remove Node 8 references and some dead code (#9284) Dec 9, 2019
testSetupFile.js chore: goodbye AppVeyor, it was a good ride (#7660) Mar 19, 2019
tsconfig.json chore: remove esModuleInterop (#8861) Aug 22, 2019
yarn.lock chore(lint): enable `eslint-comments/no-unused-disable` (#9241) Nov 30, 2019

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🃏 Delightful JavaScript Testing

👩🏻‍💻 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 on

Table of Contents

Getting Started

Install Jest using yarn:

yarn add --dev jest

Or npm:

npm install --save-dev jest

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 adds two numbers. First, create a sum.js file:

function sum(a, b) {
  return a + b;
module.exports = sum;

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

const sum = require('./sum');

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

Add the following section to your package.json:

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

Finally, run yarn test or npm run 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 used expect and toBe to test that two values were exactly identical. To learn about the other things that Jest can test, see Using Matchers.

Running from command line

You can run Jest directly from the CLI (if it's globally available in your PATH, e.g. by yarn global add jest or npm install jest --global) with a variety of useful options.

Here's how to run Jest on files matching my-test, using config.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 running jest through the command line, take a look at the Jest CLI Options page.

Additional Configuration

Generate a basic configuration file

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:

jest --init

Using Babel

To use Babel, install required dependencies via yarn:

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

If you do not already have babel configured for your project, you can use Babel to target your current version of Node by creating a babel.config.js file in the root of your project:

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

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

Making your Babel config jest-aware

Jest will set process.env.NODE_ENV to 'test' if it's not set to something else. You can use that in your configuration to conditionally setup only the compilation needed for Jest, e.g.

// babel.config.js
module.exports = api => {
  const isTest = api.env('test');
  // You can use isTest to determine what presets and plugins to use.

  return {
    // ...

Note: babel-jest is automatically installed when installing Jest and will automatically transform files if a babel configuration exists in your project. To avoid this behavior, you can explicitly reset the transform configuration option:

// jest.config.js
module.exports = {
  transform: {},

Using webpack

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.

Using TypeScript

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

yarn add --dev @babel/preset-typescript

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

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

Note, there are some caveats to using TypeScript with Babel. Because TypeScript support in Babel is transpilation, Jest will not type-check your tests as they are run. If you want that, you can use ts-jest.


Learn more about using Jest on the official site!


Show the world you're using Jest tested with jest jest

[![tested with jest](]( [![jest](](


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.

Code of Conduct

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

Contributing Guide

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

Good First Issues

To help you get your feet wet and get you familiar with our contribution process, we have a list of good 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 who contribute.


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 is MIT licensed.

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