At least it's somewhat possible to reliably test behavior of these against GNU coreutils. Pull down some archaic C++ project with a pile of janky shell scripts involved in the build (Chromium might be a good target) and compare final results.
One could argue that building Gentoo is an excellent way to exercise things:) Which, granted, is kinda cheating since you could just `emerge chromium` or whatever... but IMHO even just making portage itself happy is a good first step.
