Yeah, I didn't think of it as a mere test for whether the function is present or not - though the thread title does imply that... lol
Still, getting "Helpful" as the result for a spell known as harmful being tested against IsHarmfulSpell might mean either that the function were present but bugged
or that the function weren't there at all. Then again, the later case would also raise a Lua error, thus alerting you to the function being amiss, so...
Well, at least, like you said, it might prevent false results "in case someone decided to use" the code.