How to test Express routes with Jest and Supertest

Testing Express Routes with Supertest

Supertest lets you fire real HTTP requests against your Express app without starting a server on a port. Jest provides the test runner and assertions.

npm install --save-dev jest supertest

app.js — export without listening

const express = require('express');
const app = express();
app.use(express.json());

app.get('/health', (req, res) => res.json({ status: 'ok' }));
app.post('/users', (req, res) => {
  if (!req.body.name) return res.status(400).json({ error: 'name required' });
  res.status(201).json({ id: 1, name: req.body.name });
});

module.exports = app;

tests/app.test.js

const request = require('supertest');
const app = require('../app');

describe('Health check', () => {
  it('GET /health returns 200 with status ok', async () => {
    const res = await request(app).get('/health');
    expect(res.statusCode).toBe(200);
    expect(res.body.status).toBe('ok');
  });
});

describe('POST /users', () => {
  it('creates a user when name is provided', async () => {
    const res = await request(app)
      .post('/users')
      .send({ name: 'Alice' })
      .set('Content-Type', 'application/json');
    expect(res.statusCode).toBe(201);
    expect(res.body.name).toBe('Alice');
  });

  it('returns 400 when name is missing', async () => {
    const res = await request(app).post('/users').send({});
    expect(res.statusCode).toBe(400);
  });
});

Run tests: npx jest. Add "test": "jest" to package.json scripts.