API Test Generator

API Test Generator

Generate production-grade integration tests for existing API endpoints and backend services. This skill ensures that newly provisioned schemas and controllers are fully validated against business requirements.

🎯 When to Use

• After using the forge skill to scaffold a new backend.
• When adding new endpoints to an existing service.
• When refactoring DTOs, Schemas, or ORM models.
• When generating Postman/Bruno collections for manual API testing.

🛠️ Step-by-Step Workflow

1. Analyze the Backend Structure

• Scan the existing codebase to identify the framework (e.g., Express + TS, FastAPI, Spring Boot, .NET).
• Identify the ORM being used (e.g., Prisma, SQLAlchemy, EF Core).
• Locate the router/controller files to extract the exact endpoint paths, HTTP methods, and expected payloads.

2. Set Up the Test Environment

• Generate the necessary test scaffolding (e.g., jest.config.js with ts-jest for TypeScript, or conftest.py for Pytest).
• Auto-generate test database setup, teardown, and seeding scripts using the existing ORM. Tests should run against an isolated test database (e.g., a local Docker container) and rollback state between tests.
• Provide instructions or a workflow snippet for running the tests (e.g., npm run test:e2e).

3. Generate Integration Tests

For every identified endpoint, generate tests that cover:

• Happy Path: 200 OK or 201 Created with valid payloads. Verify the response shape against the API contract.
• Validation Errors: 400 Bad Request triggers by sending missing required fields, incorrect types, or boundary violations.
• Not Found / Edge Cases: 404 Not Found handling for invalid IDs.
• Auth / Permissions (if applicable): 401 Unauthorized or 403 Forbidden checks.

Example TypeScript + Jest + Supertest:

import request from 'supertest';
import { app } from '../src/app';
import { prisma } from '../src/db/prisma';

describe('POST /api/users', () => {
  afterAll(async () => {
    await prisma.user.deleteMany(); // cleanup
  });

  it('should create a new user and return 201', async () => {
    const res = await request(app)
      .post('/api/users')
      .send({ email: 'test@example.com', name: 'Test User' });
    
    expect(res.status).toBe(201);
    expect(res.body).toHaveProperty('id');
    expect(res.body.email).toBe('test@example.com');
  });

  it('should return 400 if email is missing', async () => {
    const res = await request(app)
      .post('/api/users')
      .send({ name: 'Test User' });
    
    expect(res.status).toBe(400);
  });
});

4. Provide API Collections (Optional)

If requested, output a JSON collection for Postman or Bruno. This allows the user to easily import the endpoints and play with them manually. Make sure to parameterize base URLs using environment variables like {{baseUrl}}.

⚙️ Best Practices

• Never mock the database for integration tests if it can be avoided. Tests should hit a real test database instance to ensure ORM queries behave exactly as they will in production.
• Clear state between tests. Use ORM capabilities to truncate tables or rollback transactions before every test case to prevent flakiness.
• Use factories. Leverage libraries like faker.js or factory_boy to create realistic test payloads instead of hardcoding 'test' everywhere.