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
I guess this is a good argument for sticking with the rspec stubbing instead of using factory girl. We could just drop factory girl, or we could make sure the wiki for testing elaborates on confusions like this one.