?? Unit Testing in Node.js: Jest vs Mocha - A Practical Guide

After implementing 100+ test suites across multiple Node.js projects, here's what you need to know about choosing and implementing the right testing framework.

?? Quick Comparison:

Jest:

// Jest Example
describe('User API', () => {
  test('should create new user', async () => {
    const user = { name: 'John' };
    const response = await createUser(user);
    expect(response.status).toBe(200);
    expect(response.body).toMatchObject(user);
  });
});        

Mocha + Chai:

// Mocha Example
describe('User API', () => {
  it('should create new user', async () => {
    const user = { name: 'John' };
    const response = await createUser(user);
    expect(response).to.have.status(200);
    expect(response.body).to.deep.equal(user);
  });
});        

?? Key Differences:

1. Setup

• Jest: Zero config, built-in assertions
• Mocha: Requires chai/assert, more flexible

2. Performance

• Jest: Parallel testing by default
• Mocha: Sequential by default, parallel with setup

3. Mocking

// Jest Mocking
jest.spyOn(userService, 'create');
expect(userService.create).toHaveBeenCalledWith(userData);

// Mocha/Sinon Mocking
sinon.spy(userService, 'create');
expect(userService.create.calledWith(userData)).to.be.true;        

?? Best Practices:

1. Test Structure

describe('OrderService', () => {
  beforeEach(() => {
    // Setup test database
    // Reset mocks
  });

  it('should calculate total with tax', () => {
    const order = new Order(items);
    expect(order.getTotal()).toBe(expectedTotal);
  });

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

2. Mock External Dependencies

  jest.mock('./database', () => ({
  query: jest.fn().mockResolvedValue([/* test data */])
}));        

3. Test Coverage Goals

# Add to package.json
{
  "scripts": {
    "test": "jest --coverage --coverageThreshold=80"
  }
}        

?? Pro Tip: Use Jest for new projects (batteries included), Mocha for existing projects or when you need more flexibility.

?? Which testing framework does your team use and why?

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