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Versão: 29.7

Iniciando

Instale Jest usando seu gerenciador de pacotes favorito:

npm install --save-dev jest

Vamos começar por escrever um teste para uma função hipotética que soma dois números. First, create a sum.js file:

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

Then, create a file named sum.test.js. Este irá conter o nosso teste real:

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.

Executando a partir da linha de comando​

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.

Configuração adicional​

Gerando um arquivo de configuração básico​

Com base no seu projeto, o Jest fará algumas perguntas e irá criar um arquivo básico de configuração com uma breve descrição para cada opção:

npm init jest@latest

Usando 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'}}]],
};

A configuração ideal para o Babel dependerá do seu projeto. 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. Você pode usar isso em sua configuração para configurar condicionalmente apenas a compilação necessária para Jest, por exemplo.

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: {},
};

Usando webpack​

Jest can be used in projects that use webpack to manage assets, styles, and compilation. webpack oferece alguns desafios únicos em relação à outras ferramentas. Refer to the webpack guide to get started.

Usando 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.

Usando Parcel​

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

Usando TypeScript​

Via babel​

O Jest suporta 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. Como o suporte para TypeScript em Babel é puramente transpilação, Jest não irá checar seus testes enquanto eles são executados. 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.

Definições de tipo​

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

Você pode usar as definições de tipo que já vem com o Jest e serão atualizadas a cada vez que você atualizar o Jest. Install the @jest/globals package:

npm install --save-dev @jest/globals

E importe as APIs de:

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. Ele fornece tipos para os globais do Jest sem necessidade de importá-los.

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

@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.

Usando 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
      }
    }
  ]
}