what grade are you doing? i guess you would be doing the earlier grades since you are asking about this.
hmm the earlier ones are easy, they will play a very simple melody, and you have to sing back from memory. and there's clapping the rhythm and identifying the time signature too.
the later grades are abit tougher, there's more of aural awareness. the singing parts are also more difficult, for one, there's sight singing, where they give u quite a few notes, they give u the tonic note, and you have to sing all the notes just from the tonic notes. the passage you are supposed to memorize to sing is also much longer.
However during the test, most passages are played to you twice, so you have more time to familiarize. Basically, if you're not afraid to sing, this should not be much of a task. I think most people's worries is the sight reading section.
