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Version : 29.7

Premiers pas

Installez Jest en utilisant votre gestionnaire de paquets favori :

npm install --save-dev jest

Commençons par écrire un test pour une hypothétique fonction qui additionne deux nombres. First, create a sum.js file:

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

Then, create a file named sum.test.js. Il s'agit de notre test actuel :

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 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.

Exécution en mode ligne de commande​

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.

Configuration additionnelle​

Générez un fichier de configuration de base​

Basé sur votre projet, Jest vous posera quelques questions et créera un fichier de configuration de base avec une courte description pour chaque option :

npm init jest@latest

Utilisez Babel​

To use Babel, install required dependencies:

npm install --save-dev babel-jest @babel/core @babel/preset-env

Configure 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'}}]],
};

La configuration idéale pour Babel dépendra de votre projet. 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. Vous pouvez l'utiliser dans votre configuration pour paramétrer de manière conditionnelle uniquement la compilation nécessaire pour Jest, par exemple.

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

  return {
    // ...
  };
};
remarque

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: {},
};

Utilisez Webpack​

Jest can be used in projects that use webpack to manage assets, styles, and compilation. webpack offre quelques défis singuliers par rapport à d'autres outils. Refer to the webpack guide to get started.

Utilisation de Vite​

Jest can be used in projects that use vite to serve 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 the plugin system from vite works, but there are some working examples for first-class jest integration using vite-jest, since this is not fully supported, you might as well read the limitation of the vite-jest. Refer to the vite guide to get started.

Utilisation de Parcel​

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

Utilisez TypeScript​

Via babel​

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

npm install --save-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',
  ],
};

However, there are some caveats to using TypeScript with Babel. La prise en charge de TypeScript dans Babel étant purement une transpilation, Jest ne vérifiera pas le typage de vos tests lors de leur exécution. 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 that lets you use Jest to test projects written in TypeScript.

npm install --save-dev ts-jest

In order for Jest to transpile TypeScript with ts-jest, you may also need to create a configuration file.

Définitions de type​

There are two ways to have Jest global APIs typed for test files written in TypeScript.

Vous pouvez utiliser les définitions de types qui sont livrées avec Jest et seront mises à jour chaque fois que vous mettez à jour Jest. Install the @jest/globals package:

npm install --save-dev @jest/globals

Et importez les API depuis le paquet :

sum.test.ts
import {describe, expect, test} from '@jest/globals';
import {sum} from './sum';

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

See the additional usage documentation of describe.each/test.each and mock functions.

Or you may choose to install the @types/jest package. Il fournit des types pour les globales Jest sans devoir les importer.

npm install --save-dev @types/jest
info

@types/jest is a third party library maintained at DefinitelyTyped, hence the latest Jest features or versions may not be covered yet. Try to match versions of Jest and @types/jest as closely as possible. For example, if you are using Jest 27.4.0 then installing 27.4.x of @types/jest is ideal.

Using ESLint​

Jest can be used with ESLint without any further configuration as long as you import the Jest global helpers (describe, it, etc.) from @jest/globals before using them in your test file. This is necessary to avoid no-undef errors from ESLint, which doesn't know about the Jest globals.

If you'd like to avoid these imports, you can configure your ESLint environment to support these globals by adding the jest environment:

{
  "overrides": [
    {
      "files": ["tests/**/*"],
      "env": {
        "jest": true
      }
    }
  ]
}

Or use eslint-plugin-jest, which has a similar effect:

{
  "overrides": [
    {
      "files": ["tests/**/*"],
      "plugins": ["jest"],
      "env": {
        "jest/globals": true
      }
    }
  ]
}