Monday, January 30, 2012

Testing a jQuery Plugin with ExpectThat and Mocha

A couple of weeks ago, I announced a CoffeeScript/JavaScript assertion library called ExpectThat. In this post, I'll provide a more real-world example of how ExpectThat can be used. For this example, I'll be using the jQuery plugin and tests from one of Josh Bush's posts entitled "Testing jQuery Plugins with Node.js and Jasmine".

The jQuery plugin

The code that follows is a re-write (in CoffeeScript) of the simple jQuery plugin that Josh provided in his post.

This jQuery plugin provides a basic watermark type of feature for an input box.

The specs

Since Josh has already done the work of writing the specs for this jQuery plugin, all that I need to do is port this to CoffeeScript and add in ExpectThat. To mix things up a bit, I've chosen to use Mocha instead of Jasmine (though ExpectThat works just as well for Jasmine). For simplicity, I've combined the spec files from Josh's post.

Apples to apples 

Here's a quick before and after comparison (with both examples in CoffeeScript):

Before ExpectThat:
    describe "when calling placeholder plugin", ->
      it "should show placeholder value", ->
After ExpectThat:
    describe "when calling placeholder plugin", ->
      expectThat -> input.val().should equal "foo"
Josh's tests are already very readable, but by adding ExpectThat, I'm able to eliminate 1 line from every test and allow each to be self-documenting.

An example of the result of running the specs in the browser is shown below:

Wait, what about Node?

"So", you say, "this is great, but Josh's post was all about using the same code and specs from the browser in Node.js". Ah, yes, thanks for reminding me. It's pretty simple to run these same specs in Node.

Here are the steps:

1. Use NPM to install mocha at a global level (i.e. npm install mocha -g) then install jsdom, jquery, and expectThat.mocha at the local level (i.e. npm install <package name>).

2. Create a file called with the code shown below and compile it however you choose (i.e. "coffee --compile --output lib/ specs/").

3. Run the tests with a command such as "mocha 'lib/runspecs.js' --reporter spec" and you should see something like the following:
In future posts, I'll show how to do similar testing with other tools such as Jasmine-Node and Zombie.js. To learn more about ExpectThat, get involved, and/or keep an eye on its progress, go to


  1. I’m just figuring out what dofollow and nofollow is and how I can get backlinks. For me there’s a whole world of new information and possibilities opening up. Very interesting.

  2. Dan, you continue to awe do you manage so many things so are definetely an inspiration for me....

  3. You are too kind my friend! I have a feeling that you'll be passing me up in the not too distant future :)