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 think the best practice for using this kind of context is to define another subject in this new context, and use one-liner examples. Something like:
```ruby
context 'when somethings are specified' do
  subject do
    build_stubbed(
      :group,
      group_name: 'g2markus'
      repo_name: 'g2markus')
  end

  its(:group_name) { should eq 'g2markus' }
  its(:repo_name) { should eq 'g2markus' }
end
```
And same applies to the case when they are not specified.