This evening, the only major advantage is that it's done and it works.

The only other advantage that I can offer is that this code is about as concise and self-explanatory that I know of to setup a mock:

````
r.stubs(:user_agent).returns user_agent
````

I want to stub the request's user_agent to return this user_agent.  

There are other libraries to do the same thing, I have no doubt.  I just don't know them as well, and at this point it's a matter of personal preference.  I won't be upset if you replace this for another, or if you want to hand-code the mocks.  Your call, but I'll stick with Mocha until that call is made.