Any rules on tests needing to have like a decent average ..?

Sooo one of my classes the test average was 45 percent. Which is crazy low. And I feel like there should be some sort of rule about that being a bad test. Cause I mean to me that suggests a poorly written test instead of most of the class just not studying.

A bunch of students dropped so now the average is 55 and like I still think that's too low

Does anyone know ?