Three functions of exams
Independently on intentions,
an exam fulfills the following three functions:
For a specific exam, this function may be
amplified by a value attached to the exam: the most influential are exams
which play an important role in the life career
(say, if the enrollment to a college depends on its result).
Students are smart. They tend to learn exactly what is needed at an exam. What is not needed, is not studied.
Often this most important function is not taken into account. I doubt if it is seriously taken into account on the national levels. Often it is not taken into account even on the level of a single program in a college.
It is not difficult to realize what would be consequences of a change in an exam. However, to this end at least the question should be posed. Otherwise, people just follow an established practice and take the luxury not to think about implications.
An exam is expected to differentiate students, to assign grades to them.
I heard about these three functions of exams long ago,
from my teacher Vladimir Abramovich Rokhlin.
He did not refer to anyone,
but just mentioned as a self-obvious common sense wisdom,
then added: only the second function is commonly anticipated.
The second function is of prime value from the viewpoint of a student.
Many people, including those responsible for educational systems,
never overgrow this level of understanding
and never notice the other two functions.