You're right of course that there is an degree of fuzziness in the conversion of a method return value to a string. However, you have to assume some conversion in order to give the student an example of the value that their method should return, as in "Your function should return the value 23". Passing the return value as a parameter to println is the easiest conversion but it's over to the question author to choose whatever conversion suits them. Occasionally we do add extra test cases (usually hidden ones, or at least ones that display only if they fail) that check the type of the value returned by the method/function.