We should probably drop `--build_dir` in favor of `O`. Additionally, it would probably be good to support other make flags/variables like `V`. It would also be good to make `make kunit` call kunit_tool (tools/testing/kunit/kunit.py run). See https://groups.google.com/d/msg/kunit-dev/QmA27YEgEgI/vws1HtkpCgAJ for more information.
I believe this has been effectively resolved by https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git/commit/?h=kunit&id=0476e69f39377192d638c459d11400c6e9a6ffb0