Refactor gui_spec.rb to solve issue #29

I'm beginner on RSpec. 
So don't merge it before discussing the issue with someone more experienced than me.
I just made this pull request to "show" this code and put it on discussion.

The reasoning of this pull request of mine is:
- I thought the issue was overcomplicated using doubles (mocks/stubs)
- As a beginner on RSpec I thought Mocks/Stubs were more useful when "faking" something that you can't instantiate at test time or at least is too long (execution time) or unreliable as database access, file writings, internet comunications. So I couldn't see the point in "doubling" things that you should instantiate (at almost the same execution time cost as "doubling" it).
- Perhaps the advantage of double is to "isolate" each test and test ONLY that particular thing you're wanting too. For example, if I have some problem on Gui class all 4 examples will fail, when you probably would want it to fail on ONLY one particular test, as the others don't rely on the actual object but rely on a double. Is it what you are willing to accomplish?

**Update** - discussed and now using doubles and let.