The absolute beginner guide to unit testing in node.js

Intro

In this tutorial, we will focus on testing a simple module.

The best way to explain something is by practice. We will create a simple module in javascript and then we will test it.

Module

Let's create a simple module named append world.

• Create a folder named simple-module
• Run inside the folder npm init -y

This will create the package.json file

• Create a file called append-world.js

With the following code:

// append-world.js

'use strict';

function appendWorld(str) {
  return `${str} World`;
}

module.exports = appendWorld;

Now let's create a unit test for our module.

Unit test

The first thing we need to install our test runner.

A test runner is a very simple program that executes our tests and shows the results.

For this tutorial, we will use mocha

• Run npm install mocha --save-dev

Next we need to create a test folder.

• Create the test folder
• Inside test/ create append-world.test.js file

// test/append-world.test.js

'use strict';

const assert = require('assert');
const appendWorld = require('../append-world.js');

describe('appendWorld', () => {

  it('should append world to the end of each string', () => {
      const str = 'Hello';
      const expected = 'Hello World';

      assert.equal(appendWorld(str), expected);
  });
});

Now what we can do is to edit the package.json file and add there the following line.

"scripts": {
    "test": "mocha --recursive"
},

After we can run our tests by simply using the following command:

$ npm test

mocha --recursive

 appendWorld
    ✓ should append world to the end of each string

And we will get the output of our tests in the console.