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
  }
}

tsconfig.test.json (test-specific):

{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "types": ["jest", "node", "@testing-library/jest-dom"]
  },
  "include": ["src/**/*.test.ts", "src/**/*.spec.ts", "src/**/__tests__/**"]
}

4. Package.json Scripts

{
  "scripts": {
    "test": "jest",
    "test:watch": "jest --watch",
    "test:coverage": "jest --coverage",
    "test:ci": "jest --ci --coverage --maxWorkers=2"
  }
}

Core Testing Patterns

Basic Test Structure

import { describe, it, expect, beforeEach, afterEach } from '@jest/globals';

describe('Calculator', () => {
  let calculator: Calculator;

  beforeEach(() => {
    calculator = new Calculator();
  });

  afterEach(() => {
    // Cleanup
  });

  it('adds two numbers correctly', () => {
    const result = calculator.add(2, 3);
    expect(result).toBe(5);
  });

  it('handles negative numbers', () => {
    expect(calculator.add(-5, 3)).toBe(-2);
  });

  it.each([
    [1, 1, 2],
    [2, 3, 5],
    [10, -5, 5],
  ])('adds %i + %i to equal %i', (a, b, expected) => {
    expect(calculator.add(a, b)).toBe(expected);
  });
});

TypeScript Type-Safe Tests

interface User {
  id: number;
  name: string;
  email: string;
  role: 'admin' | 'user';
}

describe('User Service', () => {
  it('creates user with correct types', () => {
    const user: User = {
      id: 1,
      name: 'Alice',
      email: '[email protected]',
      role: 'admin',
    };

    // Type-safe assertions
    expect(user.id).toEqual(expect.any(Number));
    expect(user.name).toEqual(expect.any(String));
    expect(user.role).toMatch(/^(admin|user)$/)
how to use jest-typescript
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How to use jest-typescript on Cursor
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1
Prerequisites
Before installing skills in Cursor, ensure your development environment meets these requirements:
›Cursor installed and configured on your development machine
›Node.js version 16.0+ with npm package manager (verify with node --version)
›Active project directory or workspace where you want to add jest-typescript
2
Execute installation command
Execute the skills CLI command in your project's root directory to begin installation:
$npx skills add https://github.com/bobmatnyc/claude-mpm-skills --skill jest-typescriptcopy
The skills CLI fetches jest-typescript from GitHub repository bobmatnyc/claude-mpm-skills and configures it for Cursor.
3
Select Cursor when prompted
The CLI will show a list of available agents. Use arrow keys to navigate and space to select Cursor:
◆ Which agents do you want to install to?
│
│ ── Universal (.agents/skills) ── always included ────
│   • Amp
│   • Antigravity
│   • Cline
│   • Codex
│ ●Cursor(selected)
│   • Cursor
│   • Windsurf
4
Verify installation
Confirm successful installation by checking the skill directory location:
.cursor/skills/jest-typescript
Reload or restart Cursor to activate jest-typescript. Access the skill through slash commands (e.g., /jest-typescript) or your agent's skill management interface.
⚠
Security & Verification Notice
We perform automated surface-level scans (Gen AI Scanner, Socket, Snyk) during installation. These checks detect common vulnerabilities but do not guarantee complete security. Always review skill source code and verify the publisher's reputation before production use.
Skills execute code in your development environment. Always verify the publisher's identity, review recent commits, and test in isolated environments before production deployment.
Additional Resources
›View source code on GitHub›Skills CLI documentation›Learn more about Cursor›What are agent skills?