Developer Toolkit - Essential Developer Tools Collection

API Testing Fundamentals

API testing validates the functionality, reliability, performance, and security of Application Programming Interfaces. Unlike UI testing, API testing focuses on the business logic layer, providing faster feedback and more stable test results.

Why API Testing Matters

Early Bug Detection: Catch issues before UI development
Faster Execution: API tests run 10-100x faster than UI tests
Better Coverage: Test business logic independently
Stable Tests: Less flaky than UI automation
Integration Validation: Verify system interactions

API Testing Pyramid

E2E Tests (Few)

API/Integration Tests (Many)

Unit Tests (Most)

Types of API Testing

Functional Testing

Validates that the API works according to specifications and business requirements.

1// Example: Testing user creation API
2const response = await fetch('/api/users', {
3  method: 'POST',
4  headers: {
5    'Content-Type': 'application/json',
6    'Authorization': 'Bearer ' + token
7  },
8  body: JSON.stringify({
9    name: 'John Doe',
10    email: 'john@example.com',
11    password: 'SecurePass123!'
12  })
13});
14
15// Functional test assertions
16expect(response.status).toBe(201);
17expect(response.headers.get('content-type')).toContain('application/json');
18
19const user = await response.json();
20expect(user).toHaveProperty('id');
21expect(user.name).toBe('John Doe');
22expect(user.email).toBe('john@example.com');
23expect(user).not.toHaveProperty('password'); // Sensitive data excluded

Testing Strategies

Test Data Management

Test Data Isolation

Each test should use independent data to avoid conflicts

1// Generate unique test data
2const generateTestUser = () => ({
3  name: `Test User ${Date.now()}`,
4  email: `test${Date.now()}@example.com`,
5  password: 'TestPass123!'
6});
7
8// Use factories for consistent test data
9const userFactory = {
10  valid: () => generateTestUser(),
11  withoutEmail: () => ({ ...generateTestUser(), email: undefined }),
12  withInvalidEmail: () => ({ ...generateTestUser(), email: 'invalid-email' })
13};

Database Cleanup

Clean up test data after each test

1// Jest example with cleanup
2describe('User API', () => {
3  let createdUsers = [];
4
5  afterEach(async () => {
6    // Clean up created test data
7    for (const user of createdUsers) {
8      await deleteUser(user.id);
9    }
10    createdUsers = [];
11  });
12
13  test('should create user', async () => {
14    const user = await createUser(userFactory.valid());
15    createdUsers.push(user);
16    
17    expect(user).toHaveProperty('id');
18  });
19});

Error Testing Strategies

1// Test various error scenarios
2describe('Error Handling', () => {
3  test('should return 400 for invalid input', async () => {
4    const response = await fetch('/api/users', {
5      method: 'POST',
6      headers: { 'Content-Type': 'application/json' },
7      body: JSON.stringify({
8        name: '', // Invalid: empty name
9        email: 'invalid-email' // Invalid: malformed email
10      })
11    });
12
13    expect(response.status).toBe(400);
14    const error = await response.json();
15    expect(error.errors).toContain('Name is required');
16    expect(error.errors).toContain('Invalid email format');
17  });
18
19  test('should return 401 for unauthorized access', async () => {
20    const response = await fetch('/api/users', {
21      method: 'POST',
22      headers: { 'Content-Type': 'application/json' },
23      // No Authorization header
24      body: JSON.stringify(userFactory.valid())
25    });
26
27    expect(response.status).toBe(401);
28  });
29
30  test('should return 409 for duplicate email', async () => {
31    const userData = userFactory.valid();
32    
33    // Create user first time
34    await createUser(userData);
35    
36    // Try to create same user again
37    const response = await fetch('/api/users', {
38      method: 'POST',
39      headers: { 'Content-Type': 'application/json' },
40      body: JSON.stringify(userData)
41    });
42
43    expect(response.status).toBe(409);
44  });
45});

Testing Tools and Frameworks

Popular API Testing Tools

Postman

User-friendly GUI tool for manual and automated API testing

Visual request builder
Collection management
Environment variables
Automated test scripts

Jest/Vitest

JavaScript testing frameworks with API testing capabilities

Fast test execution
Rich assertion library
Mocking capabilities
CI/CD integration

SuperTest

HTTP assertion library for Node.js applications

Express.js integration
Fluent API
Built-in assertions
Easy setup

REST Assured

Java library for REST API testing

BDD-style syntax
JSON/XML parsing
Authentication support
Powerful matchers

Testing Framework Example: Jest + SuperTest

1// Complete test suite example
2const request = require('supertest');
3const app = require('../src/app');
4const { setupTestDB, cleanupTestDB } = require('./helpers/database');
5
6describe('User API Integration Tests', () => {
7  beforeAll(async () => {
8    await setupTestDB();
9  });
10
11  afterAll(async () => {
12    await cleanupTestDB();
13  });
14
15  describe('POST /api/users', () => {
16    test('should create user successfully', async () => {
17      const userData = {
18        name: 'John Doe',
19        email: 'john@example.com',
20        password: 'SecurePass123!'
21      };
22
23      const response = await request(app)
24        .post('/api/users')
25        .send(userData)
26        .expect(201)
27        .expect('Content-Type', /json/);
28
29      expect(response.body).toMatchObject({
30        id: expect.any(Number),
31        name: userData.name,
32        email: userData.email
33      });
34      expect(response.body).not.toHaveProperty('password');
35    });
36
37    test('should validate required fields', async () => {
38      await request(app)
39        .post('/api/users')
40        .send({}) // Empty body
41        .expect(400)
42        .expect((res) => {
43          expect(res.body.errors).toContain('Name is required');
44          expect(res.body.errors).toContain('Email is required');
45        });
46    });
47  });
48
49  describe('GET /api/users/:id', () => {
50    test('should get user by ID', async () => {
51      // Create a user first
52      const createResponse = await request(app)
53        .post('/api/users')
54        .send({
55          name: 'Jane Doe',
56          email: 'jane@example.com',
57          password: 'SecurePass123!'
58        });
59
60      const userId = createResponse.body.id;
61
62      // Get the user
63      await request(app)
64        .get(`/api/users/${userId}`)
65        .expect(200)
66        .expect((res) => {
67          expect(res.body.id).toBe(userId);
68          expect(res.body.name).toBe('Jane Doe');
69        });
70    });
71
72    test('should return 404 for non-existent user', async () => {
73      await request(app)
74        .get('/api/users/99999')
75        .expect(404);
76    });
77  });
78});

API Security Testing

Security testing ensures your API protects against common vulnerabilities and unauthorized access attempts.

Authentication and Authorization Testing

1// Test authentication scenarios
2describe('Authentication Tests', () => {
3  test('should require valid token', async () => {
4    await request(app)
5      .get('/api/protected-resource')
6      .expect(401);
7  });
8
9  test('should accept valid JWT token', async () => {
10    const token = generateValidJWT({ userId: 123 });
11    
12    await request(app)
13      .get('/api/protected-resource')
14      .set('Authorization', `Bearer ${token}`)
15      .expect(200);
16  });
17
18  test('should reject expired token', async () => {
19    const expiredToken = generateExpiredJWT({ userId: 123 });
20    
21    await request(app)
22      .get('/api/protected-resource')
23      .set('Authorization', `Bearer ${expiredToken}`)
24      .expect(401);
25  });
26
27  test('should enforce role-based access', async () => {
28    const userToken = generateJWT({ userId: 123, role: 'user' });
29    
30    await request(app)
31      .get('/api/admin-only-resource')
32      .set('Authorization', `Bearer ${userToken}`)
33      .expect(403); // Forbidden
34  });
35});

Input Validation and Injection Testing

SQL Injection Testing

1// Test for SQL injection vulnerabilities
2test('should prevent SQL injection', async () => {
3  const maliciousInput = "'; DROP TABLE users; --";
4  
5  await request(app)
6    .post('/api/users/search')
7    .send({ name: maliciousInput })
8    .expect(400); // Should reject malicious input
9    
10  // Verify database is still intact
11  const users = await User.findAll();
12  expect(users).toBeDefined();
13});

XSS Prevention Testing

1// Test XSS prevention
2test('should sanitize script tags', async () => {
3  const xssPayload = '<script>alert("XSS")</script>';
4  
5  const response = await request(app)
6    .post('/api/comments')
7    .send({ content: xssPayload })
8    .expect(201);
9    
10  // Content should be sanitized
11  expect(response.body.content).not.toContain('<script>');
12  expect(response.body.content).toContain('&lt;script&gt;');
13});

Test Automation and CI/CD Integration

Continuous Integration Setup

1# GitHub Actions workflow for API testing
2name: API Tests
3on:
4  push:
5    branches: [ main, develop ]
6  pull_request:
7    branches: [ main ]
8
9jobs:
10  test:
11    runs-on: ubuntu-latest
12    
13    services:
14      postgres:
15        image: postgres:13
16        env:
17          POSTGRES_PASSWORD: postgres
18          POSTGRES_DB: test_db
19        options: >-
20          --health-cmd pg_isready
21          --health-interval 10s
22          --health-timeout 5s
23          --health-retries 5
24
25    steps:
26    - uses: actions/checkout@v3
27    
28    - name: Setup Node.js
29      uses: actions/setup-node@v3
30      with:
31        node-version: '18'
32        cache: 'npm'
33    
34    - name: Install dependencies
35      run: npm ci
36    
37    - name: Run database migrations
38      run: npm run migrate
39      env:
40        DATABASE_URL: postgres://postgres:postgres@localhost:5432/test_db
41    
42    - name: Run API tests
43      run: npm run test:api
44      env:
45        NODE_ENV: test
46        DATABASE_URL: postgres://postgres:postgres@localhost:5432/test_db
47    
48    - name: Generate test report
49      run: npm run test:report
50    
51    - name: Upload coverage
52      uses: codecov/codecov-action@v3

Test Environment Management

1// Environment-specific configuration
2const config = {
3  development: {
4    apiUrl: 'http://localhost:3000',
5    database: 'dev_db',
6    timeout: 5000
7  },
8  test: {
9    apiUrl: 'http://localhost:3001',
10    database: 'test_db',
11    timeout: 2000
12  },
13  staging: {
14    apiUrl: 'https://example.com',
15    database: 'staging_db',
16    timeout: 10000
17  },
18  production: {
19    apiUrl: 'https://example.com',
20    database: 'prod_db',
21    timeout: 15000
22  }
23};
24
25// Test configuration helper
26class TestConfig {
27  static getConfig() {
28    const env = process.env.NODE_ENV || 'development';
29    return config[env];
30  }
31  
32  static getApiUrl() {
33    return this.getConfig().apiUrl;
34  }
35  
36  static getTimeout() {
37    return this.getConfig().timeout;
38  }
39}
40
41// Usage in tests
42describe('API Tests', () => {
43  const apiUrl = TestConfig.getApiUrl();
44  const timeout = TestConfig.getTimeout();
45  
46  test('should respond within timeout', async () => {
47    const start = Date.now();
48    await request(apiUrl).get('/api/health');
49    const duration = Date.now() - start;
50    
51    expect(duration).toBeLessThan(timeout);
52  });
53});

Best Practices Summary

Test Early and Often

Integrate API testing into your development workflow from day one.

Maintain Test Independence

Each test should be able to run independently without relying on other tests.

Cover Edge Cases

Test boundary conditions, error scenarios, and unexpected inputs.

Monitor in Production

Use synthetic monitoring to continuously test APIs in production.

Test Your JSON APIs

Use our JSON formatter and validator to ensure your API responses are properly formatted and valid before testing.

JSON Formatter JWT Decoder

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