Hi Manuel:
You've touched on a couple of important tenets. Chief among these is to develop assessments that convey wheather your learning objectives have been met.
For example, some teachers may insert questions in a test "just because the student should know this". Although the information may be solid, if it's not aligned with the course objectives, then we've missed the boat. In a way, this a a form of unfairness - even if the student is not aware of it.
Regards, Barry