fix rubocop complains, activate rubocop again, add .rubocop_todo.yml

[SimonHoenscheid]

This Pull Request (PR) fixes the following issues

Fixes #9

There are 16 failed unit tests now. These are expecting stubbing now. Need to figure that out. Any hints welcome

[ananace]

receive and have_received are entirely different things; expect(Class).to receive(:method) would add a stub method onto a class, while expect(Class).to have_received(:method) only adds a spy on if an existing method has been called.

This is also seen in the messages on the allow(Class).to ... tests, since using have_received there is a no-op. (You're basically just saying "I don't mind if a method is called", which doesn't make much sense in a testing context.)

[SimonHoenscheid]

@ananace interesting. The Rubocop messages left me with the impression these were interchangeable. I will have a closer look.

[SimonHoenscheid]

I decided to exclude these checks. Pipeline is now OK.

[bastelfreak]

looks okay to me, but we don't have acceptance tests to verify it's still working. It would be nice if someone else can take a look at well.

[ananace]

I personally dislike the period at the end of line change, but not going to hold things back on styling disagreements, especially against rubocop - which I assume is what prompted the change.