Comment by no_wizard

They’re still valid even if you aren’t changing code.

The key there is caching your results. Don’t run unit tests for code that hasn’t changed.

They still serve the important purpose of checking validity of the code under test though, so if they do get modified downstream at some point and they fail you then know the changes aren’t conforming to expectations of the system.

This of course assumes people aren’t writing highly coupled tests and that is more rare than I wish it to be