Testing CoffeeScript in Rails

As I mentioned in an earlier post on testing CoffeeScript in Node.js, Mocha is a flexible and feature-rich test framework for JavaScript. It is elegant, powerful, and a joy to use. But how do you use Mocha with Rails? Faced with this obstacle, I created MochaRails.

MochaRails is a mountable Rails engine that serves a browser-based Mocha test suite, along with your development JavaScript files, via the Asset Pipeline. It loads Chai for both should- and expect-style assertions, although since Mocha is decoupled from the assertion library, you can use another assertion library if you choose (or even write your own.)

Using should-style assertions and CoffeeScript, Mocha tests are the best-looking implementation of BDD that I have ever seen in any language. For example, here are some simple tests for a Backbone.js View.

describe 'ItemView', ->

  before ->
    @itemView = new Backbone.View
      tagName: 'li'
      className: 'item'

  describe "el", ->

    it 'should return a value', ->
      expect(@itemView.el).to.exist

    it "should return an 'li' element", ->
      @itemView.el.tagName.should.equal "LI"

  describe '$el', ->

    it "should have class 'item'", ->
      @itemView.$el.hasClass('item').should.be.true

Now that's clean! It may seem almost too clean with just three tests, but once you have scores of contexts and hundreds of tests, you'll appreciate the aesthetic. Errors are colored red of course, but Mocha errors do not light up the page like a garish billboard.

Mocha also supports asynchronous code with a simple callback mechanism. I highly recommend you browse Mocha's features and give MochaRails a try.