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Version: 30.0

Начало работы

Установите Jest используя ваш любимый менеджер пакетов:

npm install --save-dev jest

Для начала напишем тест для функции, которая складывает два числа. First, create a sum.js file:

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

Then, create a file named sum.test.js. Он будет содержать сам тест:

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.

Запуск из командной строки​

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.

Дополнительная конфигурация​

Создание базового файла конфигурации​

Исходя из ваших нужд, Jest задаст вам несколько вопросов и создаст базовый файл конфигурации с кратким описанием для каждой опции:

npm init jest@latest

С использованием 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'}}]],
};

Идеальная конфигурация Babel будет зависеть от вашего проекта. 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. Вы можете использовать эту опцию, чтобы добавить настройки, которые будут использоваться только во время запуска Jest, например:

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 with bundlers​

Most of the time you do not need to do anything special to work with different bundlers - the exception is if you have some plugin or configuration which generates files or have custom file resolution rules.

С использованием Webpack​

Jest can be used in projects that use webpack to manage assets, styles, and compilation. Webpack действительно привносит некоторые особенности, способные создать проблемы программистам, в сравнении с другими инструментами. Refer to the webpack guide to get started.

Using Vite​

Jest is not supported by Vite due to incompatibilities with the Vite plugin system.

There are examples for Jest integration with Vite in the vite-jest library. However, this library is not compatible with versions of Vite later than 2.4.2.

One alternative is Vitest which has an API compatible Jest.

Using Parcel​

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

С использованием TypeScript​

Via babel​

Jest поддерживает TypeScript, через 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. Поскольку TypeScript поддерживается в Babel через транспиляцию, Jest не будет проверять типы ваших тестах когда они запущены. 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.

Определения типов​

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

И импортируйте API из него:

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);
  });
});
tip

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
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.

Использование 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:

import {defineConfig} from 'eslint/config';
import globals from 'globals';

export default defineConfig([
  {
    files: ['**/*.js'],
    languageOptions: {
      globals: {
        ...globals.jest,
      },
    },
    rules: {
      'no-unused-vars': 'warn',
      'no-undef': 'warn',
    },
  },
]);

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

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