Jest Testing Guide

What is Jest?

Jest is a JavaScript/TypeScript testing framework for unit and integration tests.

How to Use

1. Install Jest

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

2. Configure Jest

Add to package.json or create jest.config.js:

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

3. Write a Test

Create a file like __tests__/math.test.ts:

import { add } from '../utils/math';

describe('add', () => {
  it('adds two numbers', () => {
    expect(add(1, 2)).toBe(3);
  });
});

4. Run Tests

npm test

5. Test API Routes

Use node-mocks-http or supertest to simulate API requests.

Tips

• Use describe and it blocks for structure.
• Mock dependencies with jest.mock.
• Test edge cases and error handling.