Node.js comes with a built-in module called assert that can be used for testing. We can use it to write a simple test for the games service that we wrote in Chapter 5 , Building Dynamic Websites. We add the following code under gameServiceTest.js:

'use strict';

let assert = require('assert');
let service = require('./services/games.js')

// Given
service.create('firstUserId', 'testing');

// When
let games = service.availableTo('secondUserId');

// Then            
assert.equal(games.length, 1);            
let game = games[0];
assert.equal(game.setBy, 'firstUserId');
assert.equal(game.word, 'TESTING');

Note that the assert.equal function takes the actual value as the first argument and the expected value as the second argument. This is the opposite way around to JUnit's built-in Assert.Equals, and the classic-style Assert.AreEqual in NUnit. It's important to get these parameters the right way around so that they appear correctly in error messages when an...