Jest - Additional Configuration

In this section, we'll guide you through setting up Jest for various environments like TypeScript, React, Vue, and Next.js. We'll also cover additional Jest configurations for integrating with tools like Babel, Webpack, and ESLint.. This will help you test both backend and frontend applications, and integrate with other tools you already use.

Various Configuration Steps

Here we will show additional configuration with different languages, frameworks and libraries.

• TypeScript
• React
• Vue
• Next.js
• Babel
• Webpack
• ESLint

TypeScript Environment Setup with Jest

In this section, we'll show you how to set up Jest for a TypeScript project, including initializing the project, installing dependencies, configuring Jest, and writing a basic TypeScript test.

• Project Initialization: To start, create a new project directory and initialize a new Node.js project:

mkdir typescript-jest-project
cd typescript-jest-project
npm init -y

npm install --save-dev typescript
npm install --save-dev jest
npm install --save-dev ts-jest
npm install --save-dev @types/jest

npx tsc --init

module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  roots: ['<rootDir>/src'],
  transform: {
    '^.+\\.tsx?$': 'ts-jest'
  },
  testRegex: '(/__tests__/.*|(\\.|/)(test|spec))\\.tsx?$',
  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node']
};

export function multiply(a: number, b: number): number {
  return a * b;
}

import { multiply } from '../src/math';

describe('Multiplication', () => {
  test('multiplies two numbers', () => {
    expect(multiply(2, 3)).toBe(6);
  });
});

npx jest

React Environment Setup With Jest

This section covers setting up Jest in a React project. You'll learn how to create a React app, install testing libraries, and configure Jest to test React components.

• Create a React project: Start by creating a new React app with TypeScript:

npx create-react-app react-jest-project --template typescript
cd react-jest-project

# Install React Testing Libraries
npm install --save-dev @testing-library/react
npm install --save-dev @testing-library/jest-dom
npm install --save-dev @testing-library/user-event

// jest.config.js
module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'jsdom',
  setupFilesAfterEnv: ['@testing-library/jest-dom/extend-expect'],
  moduleNameMapper: {
    '\\.(css|less|scss|sass)$': 'identity-obj-proxy'
  }
};

// src/App.test.tsx
import React from 'react';
import { render, screen } from '@testing-library/react';
import App from './App';

test('renders learn react link', () => {
  render(<App />);
  const linkElement = screen.getByText(/learn react/i);
  expect(linkElement).toBeInTheDocument();
});

{
  "scripts": {
    "test": "react-scripts test",
    "test:watch": "react-scripts test --watch",
    "test:coverage": "react-scripts test --coverage"
  }
}

npm test

Vue.js Environment Setup with Jest

In this section, we'll guide you through setting up Jest in a Vue.js project with TypeScript, covering project creation, dependency installation, Jest configuration, and writing a simple test.

• Create a Vue Project with TypeScript using the Vue CLI:

vue create vue-jest-project
# navigate into the project directory
cd vue-jest-project

npm install --save-dev @vue/test-utils @vue/vue3-jest jest ts-jest

module.exports = {
  preset: '@vue/vue3-jest', // Use Vue 3 Jest preset
  testEnvironment: 'jsdom', // Test environment
  transform: {
    '^.+\\.vue$': '@vue/vue3-jest',
    '^.+\\.js$': 'babel-jest',
    '^.+\\.ts$': 'ts-jest'
  },
  testRegex: '(/__tests__/.*|(\\.|/)(test|spec))\\.(jsx?|tsx?)$' // Match test files
};

<template>
  <div>
    <h1>Hello, Vue!</h1>
  </div>
</template>

<script lang="ts">
export default {
  name: 'App'
}
</script>

import { mount } from '@vue/test-utils'
import App from '../src/App.vue'

describe('App.vue', () => {
  it('renders the correct text', () => {
    const wrapper = mount(App)
    expect(wrapper.text()).toContain('Hello, Vue!')
  })
})

npm run test

If everything is set up correctly, Jest will run the test and show the results.

Next.js Environment Setup with Jest

In this section, we'll guide you through setting up Jest in a Next.js project. This includes creating the project, installing necessary dependencies, configuring Jest, and writing a simple test.

• To start, create a new Next.js project:

npx create-next-app next-jest-project
cd next-jest-project

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

// jest.config.js
module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'jsdom',
  transform: {
    '^.+\\.tsx?$': 'ts-jest',
    '^.+\\.js$': 'babel-jest',
  },
  moduleNameMapper: {
    '\\.css$': 'identity-obj-proxy',
  },
  setupFilesAfterEnv: ['@testing-library/jest-dom/extend-expect'],
};

// components/Hello.tsx
import React from 'react';

const Hello = () => {
  return <h1>Hello, Next.js!</h1>;
};

export default Hello;

// components/Hello.test.tsx
import { render, screen } from '@testing-library/react';
import Hello from './Hello';

test('renders Hello, Next.js!', () => {
  render(<Hello />);
  const element = screen.getByText(/Hello, Next.js!/i);
  expect(element).toBeInTheDocument();
});

"scripts": {
  "test": "jest"
}

npm test

Babel Integration

If your project uses Babel to convert JavaScript code, you can configure it to work with Jest for testing.

• Install Babel Dependencies: If you haven't already installed Babel, run:

npm install --save-dev babel-jest @babel/core @babel/preset-env

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

ESLint Integration

To avoid linting issues while running tests with Jest, you can configure ESLint to understand Jest's global variables.

• Configure ESLint for Jest: In your .eslintrc.json or .eslintrc.js file, add Jest to the environment:

{
  "env": {
    "jest": true
  }
}

npm install --save-dev eslint-plugin-jest

Jest with Webpack

If your project uses Webpack for bundling, Jest will automatically work with it. However, if you face any issues, you can add the babel-jest package.

• Install Webpack Dependencies: If you're using Webpack, make sure you have babel-jest to integrate it with Jest:

npm install --save-dev babel-jest webpack