tl;dr: Changed unit tests now run be default when using the QA test tools.  --no-tests can be used to disable this functionality at runtime. 

The longer version.

I recently submitted a merge request for the QA tool to enable running changed unit tests by default and it's just been merged.

In the merge request we remove the --run-tests flag we used to require to run tests and instead replace it with a --no-tests option allowed users to skip the tests explicitly.

I've also got another merge request open that's being worked on that attempts to identify related unit tests for a patchset and run those too. This will certainly be behind a --more-tests switch to start with whilst we refine the guesswork in identifying such tests.

Martin