I thought this too before my current python project.
It doesn't even use type hints and has no tests.
When I look at something I don't know what it is, what it does, and have to debug there (mentally or actually) to even know what's happening. If I change something, a few runtime errors pop up right at the start. Others take 30 minutes.
Unit tests wouldn't help with that, because it doesn't cover the interaction of all the classes when they pass data on to each other; and they would probably take me months;
I would need integration tests, for which I first need to understand how the code works together
Data flows through functions as well... Or between classes that are injected , no hierarchies required;
Anyways I can't make wishes about how the code was written
It doesn't even use type hints and has no tests.
When I look at something I don't know what it is, what it does, and have to debug there (mentally or actually) to even know what's happening. If I change something, a few runtime errors pop up right at the start. Others take 30 minutes.