Improve testing throughout project

[aaronleopold]

Is your feature request related to a problem? Please describe.

Frankly, testing is very lacking. Some areas of Stump are rather awkward to test, so the goal of this ticket won't be to achieve some sort of 100% coverage. Rather, implement a system/pattern to make testing easier

Describe the solution you'd like

• Unit tests
• Integration tests

[aaronleopold]

https://docs.rs/axum-test/latest/axum_test/