That’s not a paradox, though, that’s just impossible instructions. There’s nothing paradoxical about impossible instructions. The teacher should have stipulate

That’s not a paradox, though, that’s just impossible instructions. There’s nothing paradoxical about impossible instructions. The teacher should have stipulated “You’ll have a test within the next X days but won’t know which day it’ll be on, or else it won’t happen at all.” The students realize that no test is a possibility, but they wrongly conclude that it’s what will happen, instead of realizing that that possibility merely makes the teacher’s instructions valid.