It should make you wonder instead about the appropriateness of testing over man(1) output, I suppose unless you're actually generating the format for use as man(1) input, in which case congratulations on your functional tests doing their job!

Personally I think ubiquitous software is even more important to have Easter eggs, because they're the most widely distributed, and we want as much joy as we could possibly have, before you know.

Almost everything had an easter egg in it back in the day. When computing was more fun and less serious.

They fell out of favor when people realized they were a security issue, because it was a code path that rarely got tested.

Easter eggs are always appropriate but it is imperative (and important) to understand how they could affect anything and everything.

Which means you need to usually make it explicit to call them (man --abba or something) than something that "surprises" the user.