Backend Testing Strategies: Unit, Integration, and E2E Tests

describe('UserService', () => {
  it('should create user with valid data', () => {
    const userData = {
      email: '[email protected]',
      name: 'Test User'
    };
    
    const user = userService.createUser(userData);
    
    expect(user.email).toBe('[email protected]');
    expect(user.id).toBeDefined();
  });
  
  it('should throw error for duplicate email', () => {
    userService.createUser({ email: '[email protected]' });
    
    expect(() => {
      userService.createUser({ email: '[email protected]' });
    }).toThrow('Email already exists');
  });
});

describe('User API', () => {
  beforeEach(async () => {
    await db.migrate.latest();
  });
  
  afterEach(async () => {
    await db.migrate.rollback();
  });
  
  it('POST /api/users should create user', async () => {
    const response = await request(app)
      .post('/api/users')
      .send({
        email: '[email protected]',
        name: 'Test User',
        password: 'password123'
      })
      .expect(201);
    
    expect(response.body.email).toBe('[email protected]');
    
    const user = await db('users').where({ email: '[email protected]' }).first();
    expect(user).toBeDefined();
  });
});

describe('User Registration Flow', () => {
  it('should complete full registration process', async () => {
    // Register user
    const registerResponse = await request(app)
      .post('/api/auth/register')
      .send({
        email: '[email protected]',
        password: 'password123'
      });
    
    expect(registerResponse.status).toBe(201);
    
    // Login
    const loginResponse = await request(app)
      .post('/api/auth/login')
      .send({
        email: '[email protected]',
        password: 'password123'
      });
    
    expect(loginResponse.status).toBe(200);
    expect(loginResponse.body.token).toBeDefined();
    
    // Access protected route
    const profileResponse = await request(app)
      .get('/api/users/me')
      .set('Authorization', `Bearer ${loginResponse.body.token}`);
    
    expect(profileResponse.status).toBe(200);
  });
});

const userFixtures = {
  validUser: {
    email: '[email protected]',
    name: 'Test User',
    password: 'password123'
  },
  adminUser: {
    email: '[email protected]',
    name: 'Admin',
    password: 'admin123',
    role: 'admin'
  }
};

function createUser(overrides = {}) {
  return {
    email: '[email protected]',
    name: 'Test User',
    password: 'password123',
    ...overrides
  };
}

// Mock external API
jest.mock('../services/paymentService', () => ({
  processPayment: jest.fn().mockResolvedValue({
    transactionId: 'tx_123',
    status: 'success'
  })
}));

// Use test database
const testDb = {
  host: process.env.TEST_DB_HOST,
  database: process.env.TEST_DB_NAME
};

// Clean database between tests
beforeEach(async () => {
  await db.raw('TRUNCATE TABLE users CASCADE');
});

// Aim for high coverage
// Focus on critical paths
// Don't obsess over 100%

// Use coverage tools
// jest --coverage
// nyc