Node.js API Testing with Supertest

What is API Testing with Supertest in Node.js?

Supertest sends real HTTP requests to an Express app without binding a port, which makes it ideal for integration-testing routes, middleware and status codes end to end.

API Testing with Supertest example

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

test('GET /api/jobs returns a list', async () => {
  const res = await request(app).get('/api/jobs').expect(200);
  assert.ok(Array.isArray(res.body.data));
});

test('POST /api/jobs rejects invalid input', async () => {
  const res = await request(app)
    .post('/api/jobs')
    .send({ title: 'x' })          // too short
    .expect(400);
  assert.equal(res.body.error, 'Validation failed');
});

test('protected route requires a token', async () => {
  await request(app).delete('/api/jobs/1').expect(401);
});

Key points to remember

• Export the app separately from the server so tests can import it without listening.
• Use an in-memory MongoDB or a dedicated test database — never the development one.
• Test the unhappy paths: 400, 401, 403, 404. Those are where bugs live.

Common mistakes with API Testing with Supertest

• Importing a file that calls app.listen, leaving the port open after tests finish.
• Tests that depend on each other’s data and fail when run in a different order.