In game making project, client wants to make the game of which the duration is short. Is the requirement, "the duration of the game should be short", non functional requirement? or functional requirement?
If the game had a timer that could be tested specifically, it would be a functional requirement.
If it's just "an average game should take no more than a minute" it's a non-functional requirement because there isn't a single function of the code that set the game length, but the game can still pass or fail.
"Short" isn't testable because it's undefined.