unit test for Surface.get_locks function

[jtoloff]

I believe I added all the tests needed to ensure the expected functionality, please let me know if there is anything I can improve upon.

[robertpfeiffer]

This needs to check for pixelarray locks as well.

[jtoloff]

How does the new commit look? Does the added test check pixelarray locks sufficiently?

[robertpfeiffer]

I just realised that there are two PRs for surface locking. I guess this is good enough for get_locks.

[MyreMylar]

I would like to see a check that test the output with more than one lock on a surface. e.g. if you call:

surface.lock()
surface.lock()
surface.lock()
output = surface.get_locks()  # this should be checked 

Otherwise it seems fine.

[MyreMylar]

Just gonna merge this anyway because it's better than what we have.