Eric, the unittests in Lib/test/test_compileall.py seems quite consistent to me, so for now I won't add anything.
About adding a method for testing the '-h' argument, now that Lib/compileall.py uses argparse, it sounds trivial.

EDIT: Kotan, I'm still of the same opinion. Anyway, I  think you should use as template test.test_compileall.CommandLineTests.test_legacy_paths: so, check for returncode and use subprocess.call instead of subprocess.Popen.