On a certain macOS 11.6.8 image, whitespace-tests.el reliably fails.
Could someone with an expensive Apple system verify?

I'll retake this opportunity to appeal to the non-zealots who believe
non-free software can co-exist, even benefit, free software, and invite
them to Commercial Emacs where automated tests run for linux, osx, and
windows, and are thus wont to catch non-portable changes as a
procedural, not ad hoc, matter.