[varjag]

Linux kernel project predates what you call traditional unit testing practices†. Its success in the first decade and a half coupled with pragmatics of hardware testing make the flow what it is now.

† Regression testing was certainly known then, but it was not a dogmatic movement yet.

[alkonaut]

I understand there are hurdles due to legacy, language, low level etc. But if 1 or 2% of a huge code base is easily testable, shouldn’t it be? At least if/when regressions are found in functionality that can be easily testable (pure functions etc) it would seem prudent to add regression tests to prevent the thing from happening again. Even in a 30 year old C code base.