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 would like the tests to look something like this:

    context 'when repository name is specified' do
      it 'sets repo_name to specified repository name' do
        expect(group.repo_name).to eq 'g2markus'   
      end 
    end

When I run the examples, I want to know what they are testing, not the exact values they are using.