Advanced Node.js

Chapter 13: Testing Node.js Applications

13.1 Unit and Integration Testing

Testing ensures code quality and prevents regressions. Use Jest, Mocha, or other testing frameworks.

// Jest example
const { sum, multiply } = require('./math');

describe('Math functions', () => {
    test('adds two numbers', () => {
        expect(sum(2, 3)).toBe(5);
    });
    
    test('multiplies two numbers', () => {
        expect(multiply(2, 3)).toBe(6);
    });
});

13.2 Testing Async Code

// Testing promises
test('fetches user data', async () => {
    const user = await fetchUser(1);
    expect(user).toHaveProperty('id');
    expect(user.id).toBe(1);
});

// Testing callbacks
test('handles callback', (done) => {
    asyncFunction((err, result) => {
        expect(err).toBeNull();
        expect(result).toBeDefined();
        done();
    });
});

13.3 Mocking

// Mock modules
jest.mock('./database');
const db = require('./database');

test('creates user', async () => {
    db.createUser.mockResolvedValue({ id: 1, name: 'John' });
    
    const user = await createUser({ name: 'John' });
    expect(db.createUser).toHaveBeenCalledWith({ name: 'John' });
    expect(user.id).toBe(1);
});

13.4 Integration Testing

// Test API endpoints
const request = require('supertest');
const app = require('./app');

describe('User API', () => {
    test('GET /users', async () => {
        const response = await request(app)
            .get('/users')
            .expect(200);
        
        expect(response.body).toBeInstanceOf(Array);
    });
    
    test('POST /users', async () => {
        const response = await request(app)
            .post('/users')
            .send({ name: 'John', email: 'john@example.com' })
            .expect(201);
        
        expect(response.body).toHaveProperty('id');
    });
});