Checker Trap

A known mistake, made purposefully or otherwise, that is intentionally left as a way to indicate if a checker (i.e. a person responsible for ensuring correctness and checking for mistakes) is doing their job. If the checker does not find the known mistake, they have fallen for the trap, suggesting that they either did not check for errors, were not thorough enough, or that they are not qualified for the task.

The checker trap is typically an obvious or common place mistake in order to provide a good indicator of checking quality. A mistake that is too obscure may lead to a false positive for failing the checker trap test.

That fool didn't even catch the checker trap... Off with his head!