Convert a spec to an explicit subject and lets.

@jlsuttles I was reading your spec and thinking it would read easier with a subject and some let variables. I don't know if you've used these before and don't like them. I will not feel bad if you don't want to use this. On one hand, I can read each one of your tests and not have to look anywhere else to know what's going on, on the other hand I have to skim through more text to know what's happening.