Testing in JavaScript (Node.js): Frameworks and Tools

Testing in JavaScript (Node.js): frameworks and tools

Quality testing is an integral part of Node.js development. It allows you to identify errors at early stages, simplifies refactoring, and increases application reliability. The JavaScript ecosystem has many frameworks and utilities for testing. In this article, we will look at the main tools, their capabilities, and provide practical examples.

1. Main types of tests

Before choosing a tool, it is important to understand what types of tests you will write:

• Unit tests — check individual functions or modules in isolation.
• Integration tests — check the interaction between several modules, a database, or external APIs.
• End-to-End (E2E) tests — simulate user actions in a browser or a full application.

2. Jest — a universal framework from Facebook

Jest is the most popular framework for testing JavaScript. It includes everything you need: a test runner, an assertion library, mocks, and built-in code coverage support.

Installation:

npm install --save-dev jest

Example of a simple unit test for an addition function:

// sum.jsfunction sum(a, b) {  return a + b;}module.exports = sum;

// sum.test.jsconst sum = require('./sum');

test('adds 1 + 2 equals 3', () => {  expect(sum(1, 2)).toBe(3);});

Running tests:

npx jest

Advantages of Jest:

• Zero configuration for React and Node projects.
• Automatic launch in watch mode.
• Built-in mocks and spies.
• Support for asynchronous code (async/await, callbacks).

3. Mocha + Chai — a flexible bundle

Mocha is a flexible test runner that does not impose an assertion library. It is most often used together with Chai — a library with a clear syntax (should, expect, assert).

Installation:

npm install --save-dev mocha chai

Example test with Chai:

// calculator.jsfunction divide(a, b) {  if (b === 0) throw new Error('Division by zero');  return a / b;}module.exports = { divide };

// test.jsconst { expect } = require('chai');const { divide } = require('./calculator');

describe('Calculator', function() {  it('should divide two numbers', function() {    expect(divide(10, 2)).to.equal(5);  });

  it('should throw error when dividing by zero', function() {    expect(() => divide(10, 0)).to.throw('Division by zero');  });});

Running:

npx mocha test.js

Mocha is especially convenient when you need fine-tuning of reports and integration with other tools.

4. Supertest — testing HTTP servers

Supertest is a library for integration testing of Express (and other) servers. It allows you to send HTTP requests and check responses.

Installation:

npm install --save-dev supertest

Example test for an Express application:

// app.jsconst express = require('express');const app = express();app.get('/hello', (req, res) => res.json({ message: 'Hello World' }));module.exports = app;

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

describe('GET /hello', function() {  it('responds with json', function(done) {    request(app)      .get('/hello')      .expect('Content-Type', /json/)      .expect(200)      .then(response => {        expect(response.body.message).toBe('Hello World');        done();      });  });});

Supertest works great with Jest or Mocha.