Add intentionally empty file to implicitly test cops on it

[fatkodima]

Here and there are error reports that some cop fails on an empty file. The latest of them - rubocop/rubocop-minitest#225. Some of the cops already have test cases for empty files, but it is tedious to write them and very often just forgotten.

So I added an empty file into the project so that cops (at least which are not disabled) are always tested (implicitly) on an empty file.
I think, we should add a similar file to the test/ directory of the rubocop-minitest gem and somewhere to the rubocop-rails too.

[bbatsov]

I get the idea, but I don't like having an empty lib file simply for test purposes (as it will look weird if someone's browsing the code). I guess we can just have the test task create and delete one or something along those lines.

[fatkodima]

That is actually the response I was expected 😄

How about moving it into the spec/ directory? Or tweaking spec/spec_helper.rb to add such a test case to all cop test suites? (not sure how to do it - not a rspec user).

[bbatsov]

Something like this would be fine by me.

[fatkodima]

Moved the file to spec/.