checkout the PPL diary in the forum, theres is quite a lot of PPL skill tests written up there (mine included!)
The examiner isn't going to expect you to repeat any of the exams in the air/before you start or anything, however he will most likely ask you relevant questions to what you are going to be doing. I was asked a number of questions whilst I was doing the preflight check..'What does this do?...Why does it do it? etc' Most of which you should know, the examiners not trying to catch you out.