Add (unit?) testing

[KingNook]

Context

When creating #13 I noticed I lack any sort of testing to ensure I haven't broken anything - at the moment my testing really does just consist of running pygbag . and mashing keys for a bit to see if anything breaks. I would like (mainly for peace of mind but also because it's good practice) to have some sort of proper testing

Thoughts / Challenges

Main issue for me personally would be my lack of knowledge / experience in designing tests - this will likely require some amount of research

Methods

Shall attempt to utilise Python's in-built unittest module (if it's there may as well use it)

[KingNook]

Also look at alternative / additional python testing modules eg doctest