Nextjs Testing Jest and React Testing Library Setting up Jest (with the Rust Compiler)

To set up Jest, install jest , @testing-library/react, @testing-library/jest-dom:

npm install --save-dev jest @testing-library/react @testing-library/jest-dom

Create a jest.config.js file in your project's root directory and add the following:

// jest.config.js
const nextJest = require('next/jest')

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 customJestConfig = {
  // Add more setup options before each test is run
  // setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
  // if using TypeScript with a baseUrl set to the root directory then you need the below for alias' to work
  moduleDirectories: ['node_modules', '<rootDir>/'],
  testEnvironment: 'jest-environment-jsdom',
}

// createJestConfig is exported this way to ensure that next/jest can load the Next.js config which is async
module.exports = createJestConfig(customJestConfig)

Nextjs Testing Jest and React Testing Library Setting up Jest (with the Rust Compiler)

To set up Jest, install jest , @testing-library/react, @testing-library/jest-dom:

npm install --save-dev jest @testing-library/react @testing-library/jest-dom

Nextjs Testing Jest and React Testing Library Setting up Jest (with the Rust Compiler)

Create a jest.config.js file in your project's root directory and add the following:

// jest.config.js
const nextJest = require('next/jest')

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 customJestConfig = {
  // Add more setup options before each test is run
  // setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
  // if using TypeScript with a baseUrl set to the root directory then you need the below for alias' to work
  moduleDirectories: ['node_modules', '<rootDir>/'],
  testEnvironment: 'jest-environment-jsdom',
}

// createJestConfig is exported this way to ensure that next/jest can load the Next.js config which is async
module.exports = createJestConfig(customJestConfig)

Nextjs Testing Jest and React Testing Library Setting up Jest (with Babel)

@testing-library/jest-dom includes a set of convenient 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:

// jest.config.js
setupFilesAfterEnv: ['<rootDir>/jest.setup.js']

Nextjs Testing Jest and React Testing Library Setting up Jest (with Babel)

Here are the recommended options to configure Jest for Next.js:

// jest.config.js
module.exports = {
  collectCoverageFrom: [
    '**/*.{js,jsx,ts,tsx}',
    '!**/*.d.ts',
    '!**/node_modules/**',
  ],
  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)$/i': `<rootDir>/__mocks__/fileMock.js`,

    // Handle module aliases
    '^@/components/(.*)$': '<rootDir>/components/$1',
  },
  // Add more setup options before each test is run
  // setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
  testPathIgnorePatterns: ['<rootDir>/node_modules/', '<rootDir>/.next/'],
  testEnvironment: 'jsdom',
  transform: {
    // Use babel-jest to transpile tests with the next/babel preset
    // https://jestjs.io/docs/configuration#transform-objectstring-pathtotransformer--pathtotransformer-object
    '^.+\\.(js|jsx|ts|tsx)$': ['babel-jest', { presets: ['next/babel'] }],
  },
  transformIgnorePatterns: [
    '/node_modules/',
    '^.+\\.module\\.(css|sass|scss)$',
  ],
}

Nextjs Testing Jest and React Testing Library Setting up Jest (with Babel)

Then, inside jest.setup.js, add the following import:

// jest.setup.js
import '@testing-library/jest-dom/extend-expect'

Nextjs Testing Jest and React Testing Library Setting up Jest (with Babel)

If your project is using 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:

// tsconfig.json or jsconfig.json
{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "@/components/*": ["components/*"]
    }
  }
}

Nextjs Testing Jest and React Testing Library Setting up Jest (with Babel)

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:

// __mocks__/fileMock.js
module.exports = {
  src: '/img.jpg',
  height: 24,
  width: 24,
  blurDataURL: 'data:image/png;base64,imagedata',
}

Nextjs Testing Jest and React Testing Library Quickstart

You can use create-next-app with the with-jest example to quickly get started with Jest and React Testing Library:

npx create-next-app@latest --example with-jest with-jest-app

Nextjs Testing Jest and React Testing Library Creating your tests:

Add the Jest executable in watch mode to the package.json scripts:

"scripts": {
  "dev": "next dev",
  "build": "next build",
  "start": "next start",
  "test": "jest --watch"
}

Nextjs Testing Jest and React Testing Library Creating your tests:

For example, we can add a test to check if the component successfully renders a heading:

// __tests__/index.test.jsx

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', {
      name: /welcome to next\.js!/i,
    })

    expect(heading).toBeInTheDocument()
  })
})

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