Node.js · Chapter 37 of 43
Testing Node.js Apps
Automated tests verify your code behaves correctly and catch regressions before they reach production. Popular Node.js testing tools include Jest, Mocha, and the built-in `node:test` module.
Unit tests check individual functions in isolation, while integration tests verify how multiple parts (like routes and databases) work together.
Writing a unit test
A test typically calls a function with known input and asserts the output matches an expected value.
Testing an API endpoint
Libraries like `supertest` let you send fake HTTP requests to an Express app and assert on the response, without starting a real server.
Example 1 (javascript)
const { test } = require('node:test');
const assert = require('assert');
function add(a, b) { return a + b; }
test('adds numbers', () => {
assert.strictEqual(add(2, 3), 5);
});Output
✔ adds numbersThe built-in node:test module runs the test and reports pass/fail.
Example 2 (javascript)
const request = require('supertest');
const app = require('./app');
request(app).get('/').expect(200).then(res => console.log(res.text));Output
200 OK, response body loggedsupertest simulates HTTP requests against the Express app in-memory for testing.
Key points
- Automated tests catch regressions before production.
- Unit tests isolate individual functions; integration tests check combined behaviour.
- node:test is Node's built-in test runner (no install needed).
- supertest is popular for testing Express routes.
💡 Note: Aim to test critical business logic and edge cases, not just the happy path.