API Test Case Generator

Supertest is a Node.js HTTP testing library built on top of superagent. It lets you make HTTP requests to your Express/Fastify/Koa app without starting a real server. You pass your app to request(app), chain HTTP methods, set headers and body, then assert on status codes, response bodies, and headers. It works seamlessly with Jest and Mocha.

For every endpoint, cover: (1) Happy path — valid input, expected 200/201 response. (2) Validation errors — missing required fields, invalid types, out-of-range values (400). (3) Authentication — no token (401), invalid token (401), insufficient permissions (403). (4) Not found — invalid ID (404). (5) Edge cases — empty strings, max length, special characters, SQL injection attempts.

Unit tests test individual functions/middleware in isolation with mocked dependencies. Integration tests test the full HTTP request/response cycle — real database, real middleware chain. For APIs, integration tests with Supertest catch real issues (SQL errors, auth middleware bugs, serialization problems) that unit tests with mocks miss. A good strategy: unit test business logic, integration test HTTP layer.

Common patterns: (1) JWT — generate a test token in beforeAll(), include it as Authorization: Bearer <token> in test requests. (2) API keys — set as env var TEST_API_KEY, include in x-api-key header. (3) Session cookies — use a helper function to log in and extract the session cookie. Store auth state in describe-level beforeAll() to avoid re-authenticating per test.

Supertest: expect(res.status).toBe(400) or chained .expect(400). For response body: expect(res.body.error).toBe('Validation failed'). For headers: expect(res.headers['content-type']).toMatch(/json/). For error cases, test both the status code AND the error message structure — this ensures your error middleware formats errors correctly and consistently.