API Contract Testing Framework

The Challenge

Technical Solution

Implemented comprehensive API contract testing using Playwright's API testing capabilities with schema validation.

import { test, expect } from '@playwright/test';
import { UserSchema } from './schemas/user.schema';

test.describe('Users API Contract', () => {
  test('GET /api/users returns valid schema', async ({ request }) => {
    const response = await request.get('/api/users');

    // Status code validation
    expect(response.status()).toBe(200);

    // Content-Type validation
    expect(response.headers()['content-type'])
      .toContain('application/json');

    // Schema validation
    const data = await response.json();
    const validation = UserSchema.safeParse(data);
    expect(validation.success).toBe(true);
  });

  test('POST /api/users validates required fields', async ({ request }) => {
    const response = await request.post('/api/users', {
      data: { email: 'invalid' } // Missing required fields
    });

    expect(response.status()).toBe(400);
  });
});

Key Implementation Details

• Schema validation using Zod for type-safe contract definitions
• Request/response header validation for content negotiation
• Error response structure validation for consistent error handling
• Authentication flow testing with token refresh scenarios
• Rate limiting and pagination contract verification

Tech Stack

Impact & Results

• Eliminated breaking changes in production through early contract violation detection
• Reduced integration testing time by 60% with automated contract validation
• Improved cross-team communication with shared contract definitions
• Faster API development with confidence in backward compatibility
• Self-documenting APIs through schema-as-code approach