Backend Testing Strategies: Unit, Integration, and E2E Tests
Comprehensive testing is essential for reliable backend systems. Here’s a guide to effective testing strategies. Testing Pyramid /\ / \ E2E Tests (Few) /____\ / \ Integration Tests (Some) /________\ / \ Unit Tests (Many) /____________\ 1. Unit Tests What to Test Individual functions Business logic Data transformations Edge cases Example 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'); }); }); 2. Integration Tests What to Test API endpoints Database operations External service interactions Service integration Example 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(); }); }); 3. End-to-End Tests What to Test Complete user workflows System integration Critical paths Example 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); }); }); 4. Test Data Management Fixtures const userFixtures = { validUser: { email: '[email protected]', name: 'Test User', password: 'password123' }, adminUser: { email: '[email protected]', name: 'Admin', password: 'admin123', role: 'admin' } }; Factories function createUser(overrides = {}) { return { email: '[email protected]', name: 'Test User', password: 'password123', ...overrides }; } 5. Mocking External Services // Mock external API jest.mock('../services/paymentService', () => ({ processPayment: jest.fn().mockResolvedValue({ transactionId: 'tx_123', status: 'success' }) })); 6. Database Testing // 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'); }); 7. Test Coverage // Aim for high coverage // Focus on critical paths // Don't obsess over 100% // Use coverage tools // jest --coverage // nyc Best Practices Write tests first (TDD) Test behavior, not implementation Keep tests independent Use descriptive test names Test edge cases Mock external dependencies Clean up test data Run tests in CI/CD Maintain test code quality Review test failures Conclusion Effective testing requires: ...