Tests are made in the tab "Tests". Both Teachers and Authors can make them.
A test is made out of the course material from the class. It can only be scheduled if the exact chapter/subchapter is available in that class.
Only Authors can make exams, in the authoring environment. 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.
Test vs Exam- Student view
Students don't see any difference between a test and an exam.