Comment by dragonwriter

The more I think about it the more I think calling it a bad example may be unfair. It can be extremely misleading for someone unfamiliar with the concept coming at it with a particular viewpoint, but I’m less sure, with more time to think, that an example that is better for that wouldn’t be worse in other ways.

I like sorting as an example, and I like that using the built-in is concise, and reimplementing the behavior of an existing function where using the existing function as an oracle is a reasonable thing to do for a test isn't all that uncommon.

I feel like something with a couple of properties described in comments with assertions testing those properties (but where the functionality and properties are familiar enough that it would make a clear connection) would be a bit better, in theory, but I don't have a great particular example to use, and anything done that way will be, at best, somewhat less concise.