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Version: 29.3

Primii pași

Install Jest using your favorite package manager:

npm install --save-dev jest

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);

Adăugați secțiunea următoare în fișierul vostru 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)

Tocmai ați scris cu succes primul test folosind Jest!

Testul acesta a folosit expect și toBe pentru a testa dacă două valori sunt identice. Pentru a afla mai multe lucruri pe care Jest le poate testa, vezi Utilizarea regulilor de potrivire.

Rularea din linia de comandă

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.

Iată cum să executaţi Jest pe fişierele my-test, folosind config.json ca fişier de configurare şi afişarea unei notificări native de sistem după rulare:

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

Dacă doriţi să aflaţi mai multe despre rularea jest prin linia de comandă, vezi pagina de Opțiuni Jest pentru linia de comandă.

Informații suplimentare

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

Folosind 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:

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.

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

return {
// ...

babel-jest is automatically installed when installing Jest and will automatically transform files if a babel configuration exists in your project. Pentru a evita acest comportament, aveţi posibilitatea să reiniţializaţi explicit opţiunea de configurare transform:

module.exports = {
transform: {},

Folosind Webpack

Jest poate fi utilizat în proiecte care folosesc webpack pentru gestionarea fișierelor statice, stiluri şi compilare. webpack oferă unele provocări unice față de alte instrumente. Urmați ghidul webpack pentru a începe.

Using 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.

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 started.

Folosind TypeScript

Via babel

Jest supports 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.

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

However, there are some caveats 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 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.

Type definitions

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

You can use type definitions which ships with Jest and will update each time you update Jest. Install the @jest/globals package:

npm install --save-dev @jest/globals

And import the testing APIs from it:

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);

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

Or you may choose to install the @types/jest package. It provides types for Jest globals without a need to import them.

npm install --save-dev @types/jest

@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.