Enter Konacha
Full transparency: Before I get into the specifics of the Konacha gem, I want to say that I'm a committer to the project. It wasn't my project, but I fell in love with it and wanted to help make it better. (I find it's always best to get that sort of thing out in the open before we move on.)
So what is Konacha, and what can it do it for us? Konacha lets you quickly set up and configure the Mocha testing framework and the Chai assertion library with Rails. Konacha gives you full access to the asset pipeline, and it allows you to customize which files you want to pull into your tests from the asset pipeline. Very conveniently, it also adds the spec/javascripts path to the list of paths that can be used by the asset pipeline, meaning that you can create support files and pull them in quite easily, much as you can do with RSpec.
In this article, we'll focus on getting Konacha installed, configured, and running. Part 2 of this series goes into details about Mocha and Chai.