We have a separate content type, called "Exam". For students, these are exactly the same as a test. So from the student perspective, you don't need to distinguish between the two.
However, there is a difference:
A test is always part of a particular (sub-)chapter and that these tests can only be scheduled in a class if that exact chapter is made available in that class.
An exam is not part of a chapter, but is specifically assigned to a class. Only after the exam has been assigned to that class (which is done by the author of that exam!) is a teacher allowed to use/schedule the exam for the students in that class.