Introducing chai

Let's discuss chai. chai is an assertion library, used with mocha. We could also use the native assertion library , but chai adds a lot of flexibility.

chai makes it a lot easier to write test definitions. Let's install chai and modify the preceding test to make it look more simple and easy to understand:

$ npm install chai -g

We passed the -g option to install it globally, since we do not have a package.json configuration.

Let's use chai in our previous test. In add.spec.js, add the following lines of code:

var expect = require('chai').expect;
var addUtility = require("./../add.js");

describe('Add', function(){
  describe('addUtility', function(){
    it('should have a sum method', function(){
expect(addUtility).to.be.an('object');
      expect(addUtility).to.have.property('sum');
    })

    it('addUtility.sum(5, 4) should return 9', function(){
expect(addUtility.sum(5, 4)).to.deep.equal(9);
    })

    it('addUtility.sum(100, 6) should return 106', function(){
expect(addUtility...