Download next.js/docs/01-app/02-guides/testing/jest.mdx from Devendra174/react-code-dataset: direct link, hf CLI and curl.
- Browser
- Download file 13 kB
-
https://huggingface.co/datasets/Devendra174/react-code-dataset/resolve/main/next.js/docs/01-app/02-guides/testing/jest.mdx
- Command line
-
hf download hf://datasets/Devendra174/react-code-dataset/next.js/docs/01-app/02-guides/testing/jest.mdx
-
curl -L -o jest.mdx https://huggingface.co/datasets/Devendra174/react-code-dataset/resolve/main/next.js/docs/01-app/02-guides/testing/jest.mdx
13 kB
| --- | |
| title: How to set up Jest with Next.js | |
| nav_title: Jest | |
| description: Learn how to set up Jest with Next.js for Unit Testing and Snapshot Testing. | |
| --- | |
| {/* The content of this doc is shared between the app and pages router. You can use the `<PagesOnly>Content</PagesOnly>` component to add content that is specific to the Pages Router. Any shared content should not be wrapped in a component. */} | |
| Jest and React Testing Library are frequently used together for **Unit Testing** and **Snapshot Testing**. This guide will show you how to set up Jest with Next.js and write your first tests. | |
| > **Good to know:** Since `async` Server Components are new to the React ecosystem, Jest currently does not support them. While you can still run **unit tests** for synchronous Server and Client Components, we recommend using an **E2E tests** for `async` components. | |
| ## Quickstart | |
| You can use `create-next-app` with the Next.js [with-jest](https://github.com/vercel/next.js/tree/canary/examples/with-jest) example to quickly get started: | |
| ```bash filename="Terminal" | |
| npx create-next-app --example with-jest with-jest-app | |
| ``` | |
| ## Manual setup | |
| Since the release of [Next.js 12](https://nextjs.org/blog/next-12), Next.js now has built-in configuration for Jest. | |
| To set up Jest, install `jest` and the following packages as dev dependencies: | |
| ```bash filename="Terminal" | |
| npm install -D jest jest-environment-jsdom -library/react -library/dom -library/jest-dom ts-node /jest | |
| # or | |
| yarn add -D jest jest-environment-jsdom -library/react -library/dom -library/jest-dom ts-node /jest | |
| # or | |
| pnpm install -D jest jest-environment-jsdom -library/react -library/dom -library/jest-dom ts-node /jest | |
| ``` | |
| Generate a basic Jest configuration file by running the following command: | |
| ```bash filename="Terminal" | |
| npm init jest | |
| # or | |
| yarn create jest | |
| # or | |
| pnpm create jest | |
| ``` | |
| This will take you through a series of prompts to setup Jest for your project, including automatically creating a `jest.config.ts|js` file. | |
| Update your config file to use `next/jest`. This transformer has all the necessary configuration options for Jest to work with Next.js: | |
| ```ts filename="jest.config.ts" switcher | |
| import type { Config } from 'jest' | |
| import nextJest from 'next/jest.js' | |
| const createJestConfig = nextJest({ | |
| // Provide the path to your Next.js app to load next.config.js and .env files in your test environment | |
| dir: './', | |
| }) | |
| // Add any custom config to be passed to Jest | |
| const config: Config = { | |
| coverageProvider: 'v8', | |
| testEnvironment: 'jsdom', | |
| // Add more setup options before each test is run | |
| // setupFilesAfterEnv: ['<rootDir>/jest.setup.ts'], | |
| } | |
| // createJestConfig is exported this way to ensure that next/jest can load the Next.js config which is async | |
| export default createJestConfig(config) | |
| ``` | |
| ```js filename="jest.config.js" switcher | |
| const nextJest = require('next/jest') | |
| /** @type {import('jest').Config} */ | |
| const createJestConfig = nextJest({ | |
| // Provide the path to your Next.js app to load next.config.js and .env files in your test environment | |
| dir: './', | |
| }) | |
| // Add any custom config to be passed to Jest | |
| const config = { | |
| coverageProvider: 'v8', | |
| testEnvironment: 'jsdom', | |
| // Add more setup options before each test is run | |
| // setupFilesAfterEnv: ['<rootDir>/jest.setup.ts'], | |
| } | |
| // createJestConfig is exported this way to ensure that next/jest can load the Next.js config which is async | |
| module.exports = createJestConfig(config) | |
| ``` | |
| Under the hood, `next/jest` is automatically configuring Jest for you, including: | |
| - Setting up `transform` using the [Next.js Compiler](/docs/architecture/nextjs-compiler). | |
| - Auto mocking stylesheets (`.css`, `.module.css`, and their scss variants), image imports and [`next/font`](/docs/app/api-reference/components/font). | |
| - Loading `.env` (and all variants) into `process.env`. | |
| - Ignoring `node_modules` from test resolving and transforms. | |
| - Ignoring `.next` from test resolving. | |
| - Loading `next.config.js` for flags that enable SWC transforms. | |
| > **Good to know**: To test environment variables directly, load them manually in a separate setup script or in your `jest.config.ts` file. For more information, please see [Test Environment Variables](/docs/app/guides/environment-variables#test-environment-variables). | |
| <PagesOnly> | |
| ## Setting up Jest (with Babel) | |
| If you opt out of the [Next.js Compiler](/docs/architecture/nextjs-compiler) and use Babel instead, you will need to manually configure Jest and install `babel-jest` and `identity-obj-proxy` in addition to the packages above. | |
| Here are the recommended options to configure Jest for Next.js: | |
| ```js filename="jest.config.js" | |
| module.exports = { | |
| collectCoverage: true, | |
| // on node 14.x coverage provider v8 offers good speed and more or less good report | |
| coverageProvider: 'v8', | |
| collectCoverageFrom: [ | |
| '**/*.{js,jsx,ts,tsx}', | |
| '!**/*.d.ts', | |
| '!**/node_modules/**', | |
| '!<rootDir>/out/**', | |
| '!<rootDir>/.next/**', | |
| '!<rootDir>/*.config.js', | |
| '!<rootDir>/coverage/**', | |
| ], | |
| moduleNameMapper: { | |
| // Handle CSS imports (with CSS modules) | |
| // https://jestjs.io/docs/webpack#mocking-css-modules | |
| '^.+\\.module\\.(css|sass|scss)$': 'identity-obj-proxy', | |
| // Handle CSS imports (without CSS modules) | |
| '^.+\\.(css|sass|scss)$': '<rootDir>/__mocks__/styleMock.js', | |
| // Handle image imports | |
| // https://jestjs.io/docs/webpack#handling-static-assets | |
| '^.+\\.(png|jpg|jpeg|gif|webp|avif|ico|bmp|svg)$': `<rootDir>/__mocks__/fileMock.js`, | |
| // Handle module aliases | |
| '^@/components/(.*)$': '<rootDir>/components/$1', | |
| // Handle @next/font | |
| '@next/font/(.*)': `<rootDir>/__mocks__/nextFontMock.js`, | |
| // Handle next/font | |
| 'next/font/(.*)': `<rootDir>/__mocks__/nextFontMock.js`, | |
| // Disable server-only | |
| 'server-only': `<rootDir>/__mocks__/empty.js`, | |
| }, | |
| // Add more setup options before each test is run | |
| // setupFilesAfterEnv: ['<rootDir>/jest.setup.js'], | |
| testPathIgnorePatterns: ['<rootDir>/node_modules/', '<rootDir>/.next/'], | |
| testEnvironment: 'jsdom', | |
| transform: { | |
| // Use babel-jest to transpile tests with the next/babel preset | |
| // https://jestjs.io/docs/configuration#transform-objectstring-pathtotransformer--pathtotransformer-object | |
| '^.+\\.(js|jsx|ts|tsx)$': ['babel-jest', { presets: ['next/babel'] }], | |
| }, | |
| transformIgnorePatterns: [ | |
| '/node_modules/', | |
| '^.+\\.module\\.(css|sass|scss)$', | |
| ], | |
| } | |
| ``` | |
| You can learn more about each configuration option in the [Jest docs](https://jestjs.io/docs/configuration). We also recommend reviewing [`next/jest` configuration](https://github.com/vercel/next.js/blob/e02fe314dcd0ae614c65b505c6daafbdeebb920e/packages/next/src/build/jest/jest.ts) to see how Next.js configures Jest. | |
| ### Handling stylesheets and image imports | |
| Stylesheets and images aren't used in the tests but importing them may cause errors, so they will need to be mocked. | |
| Create the mock files referenced in the configuration above - `fileMock.js` and `styleMock.js` - inside a `__mocks__` directory: | |
| ```js filename="__mocks__/fileMock.js" | |
| module.exports = 'test-file-stub' | |
| ``` | |
| ```js filename="__mocks__/styleMock.js" | |
| module.exports = {} | |
| ``` | |
| For more information on handling static assets, please refer to the [Jest Docs](https://jestjs.io/docs/webpack#handling-static-assets). | |
| ## Handling Fonts | |
| To handle fonts, create the `nextFontMock.js` file inside the `__mocks__` directory, and add the following configuration: | |
| ```js filename="__mocks__/nextFontMock.js" | |
| module.exports = new Proxy( | |
| {}, | |
| { | |
| get: function getter() { | |
| return () => ({ | |
| className: 'className', | |
| variable: 'variable', | |
| style: { fontFamily: 'fontFamily' }, | |
| }) | |
| }, | |
| } | |
| ) | |
| ``` | |
| </PagesOnly> | |
| ## Optional: Handling Absolute Imports and Module Path Aliases | |
| If your project is using [Module Path Aliases](/docs/app/getting-started/installation#set-up-absolute-imports-and-module-path-aliases), you will need to configure Jest to resolve the imports by matching the paths option in the `jsconfig.json` file with the `moduleNameMapper` option in the `jest.config.js` file. For example: | |
| ```json filename="tsconfig.json or jsconfig.json" | |
| { | |
| "compilerOptions": { | |
| "module": "esnext", | |
| "moduleResolution": "bundler", | |
| "baseUrl": "./", | |
| "paths": { | |
| "@/components/*": ["components/*"] | |
| } | |
| } | |
| } | |
| ``` | |
| ```js filename="jest.config.js" | |
| moduleNameMapper: { | |
| // ... | |
| '^@/components/(.*)$': '<rootDir>/components/$1', | |
| } | |
| ``` | |
| ## Optional: Extend Jest with custom matchers | |
| `@testing-library/jest-dom` includes a set of convenient [custom matchers](https://github.com/testing-library/jest-dom#custom-matchers) such as `.toBeInTheDocument()` making it easier to write tests. You can import the custom matchers for every test by adding the following option to the Jest configuration file: | |
| ```ts filename="jest.config.ts" switcher | |
| setupFilesAfterEnv: ['<rootDir>/jest.setup.ts'] | |
| ``` | |
| ```js filename="jest.config.js" switcher | |
| setupFilesAfterEnv: ['<rootDir>/jest.setup.js'] | |
| ``` | |
| Then, inside `jest.setup`, add the following import: | |
| ```ts filename="jest.setup.ts" switcher | |
| import '-library/jest-dom' | |
| ``` | |
| ```js filename="jest.setup.js" switcher | |
| import '-library/jest-dom' | |
| ``` | |
| > **Good to know:** [`extend-expect` was removed in `v6.0`](https://github.com/testing-library/jest-dom/releases/tag/v6.0.0), so if you are using `@testing-library/jest-dom` before version 6, you will need to import `@testing-library/jest-dom/extend-expect` instead. | |
| If you need to add more setup options before each test, you can add them to the `jest.setup` file above. | |
| ## Add a test script to `package.json` | |
| Finally, add a Jest `test` script to your `package.json` file: | |
| ```json filename="package.json" highlight={6-7} | |
| { | |
| "scripts": { | |
| "dev": "next dev", | |
| "build": "next build", | |
| "start": "next start", | |
| "test": "jest", | |
| "test:watch": "jest --watch" | |
| } | |
| } | |
| ``` | |
| `jest --watch` will re-run tests when a file is changed. For more Jest CLI options, please refer to the [Jest Docs](https://jestjs.io/docs/cli#reference). | |
| ### Creating your first test | |
| Your project is now ready to run tests. Create a folder called `__tests__` in your project's root directory. | |
| <PagesOnly> | |
| For example, we can add a test to check if the `<Home />` component successfully renders a heading: | |
| ```jsx filename="pages/index.js | |
| export default function Home() { | |
| return <h1>Home</h1> | |
| } | |
| ``` | |
| ```jsx filename="__tests__/index.test.js" | |
| import '@testing-library/jest-dom' | |
| import { render, screen } from '@testing-library/react' | |
| import Home from '../pages/index' | |
| describe('Home', () => { | |
| it('renders a heading', () => { | |
| render(<Home />) | |
| const heading = screen.getByRole('heading', { level: 1 }) | |
| expect(heading).toBeInTheDocument() | |
| }) | |
| }) | |
| ``` | |
| </PagesOnly> | |
| <AppOnly> | |
| For example, we can add a test to check if the `<Page />` component successfully renders a heading: | |
| ```jsx filename="app/page.js" | |
| import Link from 'next/link' | |
| export default function Page() { | |
| return ( | |
| <div> | |
| <h1>Home</h1> | |
| <Link href="/about">About</Link> | |
| </div> | |
| ) | |
| } | |
| ``` | |
| ```jsx filename="__tests__/page.test.jsx" | |
| import '@testing-library/jest-dom' | |
| import { render, screen } from '@testing-library/react' | |
| import Page from '../app/page' | |
| describe('Page', () => { | |
| it('renders a heading', () => { | |
| render(<Page />) | |
| const heading = screen.getByRole('heading', { level: 1 }) | |
| expect(heading).toBeInTheDocument() | |
| }) | |
| }) | |
| ``` | |
| </AppOnly> | |
| Optionally, add a [snapshot test](https://jestjs.io/docs/snapshot-testing) to keep track of any unexpected changes in your component: | |
| <PagesOnly> | |
| ```jsx filename="__tests__/snapshot.js" | |
| import { render } from '@testing-library/react' | |
| import Home from '../pages/index' | |
| it('renders homepage unchanged', () => { | |
| const { container } = render(<Home />) | |
| expect(container).toMatchSnapshot() | |
| }) | |
| ``` | |
| > **Good to know**: Test files should not be included inside the Pages Router because any files inside the Pages Router are considered routes. | |
| </PagesOnly> | |
| <AppOnly> | |
| ```jsx filename="__tests__/snapshot.js" | |
| import { render } from '@testing-library/react' | |
| import Page from '../app/page' | |
| it('renders homepage unchanged', () => { | |
| const { container } = render(<Page />) | |
| expect(container).toMatchSnapshot() | |
| }) | |
| ``` | |
| </AppOnly> | |
| ## Running your tests | |
| Then, run the following command to run your tests: | |
| ```bash filename="Terminal" | |
| npm run test | |
| # or | |
| yarn test | |
| # or | |
| pnpm test | |
| ``` | |
| ## Additional Resources | |
| For further reading, you may find these resources helpful: | |
| - [Next.js with Jest example](https://github.com/vercel/next.js/tree/canary/examples/with-jest) | |
| - [Jest Docs](https://jestjs.io/docs/getting-started) | |
| - [React Testing Library Docs](https://testing-library.com/docs/react-testing-library/intro/) | |
| - [Testing Playground](https://testing-playground.com/) - use good testing practices to match elements. | |