JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/chai/3.5.0/chai.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/mocha/2.4.5/mocha.min.js"></script>
<script src="https://cdn.rawgit.com/jquery/jquery/2.1.4/dist/jquery.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/mocha/2.4.5/mocha.css">
<div id="mocha"></div>

JavaScript

class Person {
  constructor(age) {
    if (Object.prototype.toString.call(age) !== '[object Number]') throw 'NOT A NUMBER'
    this.age = age;
  }
  howold() {
    console.log(this.age);
  }
}

var should = chai.should();
mocha.setup('bdd');

describe('Person', function() {
  it('should throw if input is not a number', function() {
    (function() {
      var p1 = new Person('sadf');
    }).should.not.throw;
    (function(){
    var p2= new Person('sdfa');
    }).should.throw;
  })
})

mocha.run();