jest

Jest + TypeScript - Industry Standard Testing

Overview

Jest is the industry-standard testing framework with 70% market share, providing a mature, battle-tested ecosystem for TypeScript projects. It offers comprehensive testing capabilities with built-in snapshot testing, mocking, and coverage reporting.

Key Features:

• 🏆 Industry Standard: 70% market share, widely adopted
• 📦 All-in-One: Test runner, assertions, mocks, coverage in one package
• 📸 Snapshot Testing: Built-in snapshot support for UI testing
• 🧪 React Integration: React Testing Library, enzyme compatibility
• 🔧 Mature Ecosystem: Extensive plugins, tooling, and community support
• 🎯 TypeScript Support: Full type safety via ts-jest
• 🔍 Coverage Reports: Built-in Istanbul coverage
• 🌐 Multi-Platform: Node.js, browser (jsdom), React Native

Installation:

npm install -D jest @types/jest ts-jest
npm install -D @testing-library/react @testing-library/jest-dom  # For React

Basic Setup

1. Initialize Jest Configuration

npx ts-jest config:init

This creates jest.config.js:

module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
};

2. Manual Configuration

jest.config.ts (TypeScript config):

import type { Config } from 'jest';

const config: Config = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  roots: ['<rootDir>/src'],
  testMatch: ['**/__tests__/**/*.ts', '**/?(*.)+(spec|test).ts'],
  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json'],
  collectCoverageFrom: [
    'src/**/*.{ts,tsx}',
    '!src/**/*.d.ts',
    '!src/**/*.test.{ts,tsx}',
    '!src/**/__tests__/**',
  ],
  coverageThreshold: {
    global: {
      branches: 80,
      functions: 80,
      lines: 80,
      statements: 80,
    },
  },
};

export default config;

3. TypeScript Configuration

tsconfig.json:

{
  "compilerOptions": {
    "types": ["jest", "@testing-library/jest-dom"],
    "esModuleInterop": true
  }
}