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.
(..) Another, another. Up, up. Come on. Longbottom, is it? Up. Professor Sprout tells me you have an aptitude for herbology. There's the... The Cruciatus Curse. Correct, correct. Come, come. Particularly nasty. The torture curse. (..)2005 Harry Potter and the Goblet of Fire