Switching to RSpec for testing

This is the first installment of the potential switch, it illustrates the format of model testing. If anyone has any input on how I can make these tests even better, while maintaining readability, I would really appreciate the help. I purposely only tested one method so that we can focus more on the style versus what is actually being tested. I'm hoping to decide on a style before this PR is merged.  @ferrous26 @zhangsu
As @ferrous26 suggested, why not go straight to [RSpec 3](http://myronmars.to/n/dev-blog/2014/05/notable-changes-in-rspec-3)? We would have to add the `rspec-its` gem since its been extracted out from the core.