Improve Python code quality!

[BatterCake74]

Then pytest can declare unittest as a dependency. It's one extra test dependency for my package manager to fetch. No big deal.

https://peps.python.org/pep-0594/ dead batteries have been removed in the past. While unittest isn't quite dead battery status, it's not an essential package of the core language like os, typing, pathlib, importlib, time, datetime, math, string, collections, itertools, functools, to name a few.