Add first unit tests to Gosu (#360)

[jlnr]

No description provided.

[jlnr]

@Kjarrigan I've stolen some tests from #360 and added the interface comparison I was thinking about. Still trying to get my tests to run on the Linux CI, then I'll push fixes for the red tests and merge this - and you can rebase the other tests that you have on it (calling draw_line etc. outside of Window#draw)

[jlnr]

AAHHH WTF MICROSOFT. I've wasted quite some time getting the tests to work on Windows, when they worked all along. It's just that any program that prints anything to stderr triggers an error in PowerShell, even when the exit code is 0. Windows, not even once.

[Kjarrigan]

Windows, not even once.

FullAck 😄
I'm glad that you figured that out, so the path as clear for the first gosu unit test 👍 ?!

[jlnr]

For future reference, a bit of discussion happened in this commit, which has later been rebased away: 0ec4a73#commitcomment-20396274

[Kjarrigan]

  KB_0…KB_9 = :an_integer
  KB_A…KB_Z = :an_integer

I like that new format a lot. Its definitely much cleaner than before. I still hope to get some groups in the future 😄 as I usually really just want to know the name of the button const and not the "flavour" text.
PR yard#1056