Writing API Tests in Node.js With Jest and supertest

Writing API Tests in Node.js With Jest and supertest

API tests catch bugs before users do. Here is how to write them with Jest and supertest.

Install

npm install --save-dev jest supertest. Add a test script: "test": "jest".

Set Up a Test Database

Use a separate MongoDB database for tests. Set MONGODB_URI in your test env to something like mongodb://localhost/test. Clean the database between tests.

The Basic Test

const request = require('supertest');
const app = require('../src/app');
const User = require('../src/models/user');

describe('POST /signup', () => {
  beforeEach(async () => await User.deleteMany({}));

  it('creates a user and returns 201', async () => {
    const res = await request(app)
      .post('/signup')
      .send({ firstName: 'K', email: '[email protected]', password: 'password123' });

    expect(res.status).toBe(201);
    expect(res.body.id).toBeDefined();
    expect(res.body.passwordHash).toBeUndefined();
  });

  it('returns 400 for missing fields', async () => {
    const res = await request(app)
      .post('/signup')
      .send({ email: '[email protected]' });

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

What to Test

• Happy path: the endpoint works with valid input.
• Validation errors: missing fields, wrong types, bad formats.
• Auth errors: missing or invalid token returns 401.
• Authorization errors: wrong role returns 403.
• Not found: missing resource returns 404.
• Conflict: duplicate resource returns 409.
• Pagination and filtering: list endpoints behave correctly.

Tips

• Use a fresh database or clean between tests so they are independent.
• Test status codes AND response shapes (e.g., body.id is defined).
• Do not test internal implementation; test the API contract.
• Use beforeAll and afterAll for setup and teardown.
• Run tests in CI on every push.

Auth Tests

it('returns 401 without token', async () => {
  const res = await request(app).get('/me');
  expect(res.status).toBe(401);
});

it('returns 200 with valid token', async () => {
  const login = await request(app)
    .post('/login')
    .send({ email: '[email protected]', password: 'password123' });
  const token = login.body.token;
  const res = await request(app)
    .get('/me')
    .set('Cookie', [`token=${token}`]);
  expect(res.status).toBe(200);
});

The Takeaway

Test Express APIs with Jest and supertest. Use a test database. Test happy paths and error paths. Test status codes and response shapes. Do not test internal implementation; test the API contract. Run tests in CI.