Unit testing with Mocha

Setting up Mocha

We need to install the mocha library.

npm install --save-dev mocha

Writing your first test

We use describe and it to organise our tests:

import SmartDevice from '../models/SmartDevice.js'
import { describe, it } from 'mocha'
import assert from 'assert'

describe('The SmartDevice class', function () {
  it('should be off by default', function () {
    const device = new SmartDevice()
    assert.strictEqual(device.isOn, false)
  })
})

INFO

The assert.strictEqual() method checks that the two arguments are strictly equal using javascript's ===, whereas assert.equal() uses ==. You probably want to use strictEqual the majority of the time.

Running your tests

To run your tests, add a script to your package.json file:

"scripts": {
  "test": "mocha ./test/*"
}

Then, execute npm test in your terminal.

Exploring more features

Mocha has lots and lots of features - we've just scratched the surface in this guide. When you have the opportunity, you should explore the Mocha documentation to learn more about what it can do.