a test of 'aptitude' = an 'aptitude test' [=a test that is designed to show how easily someone will be able to learn certain skills]
Anyone who can speak five languages obviously has a great natural 'aptitude' for (learning) languages.
The new test is supposed to measure the 'aptitudes' of the students.
(..) Why are you pretending to be a cop? This unit is new, and you are the newest members of it. You have been selected for it on the basis of intelligence and aptitude. This is an elite unit. Our job is to smash or marginally disrupt... ...organized crime in this city... ...by enhanced cooperation (..)2006 The Departed