I can't understand how works that code example and I think there might be others like me. So could you explain it in some more details? I think this would encrease the learning value of this meditation.
in reply to Tripwire tests and future-proofing
My hypothesis is that there should be "==" in the place of the "," (assuming that keys in scalar context will return the number of hash elements). But even with that that code would not be trivial.
Update: Another hypothesis: there should be used the is subroutine (from Test::More) instead the ok subroutine.