I think you mean de proefexamen?
I've done it at Friesland College in Sneek. You'll be given exam papers which are similar to a real exam tasks. You have to complete those tasks within a given time. It costs you nothing. They test your Listening, Writing, Speaking and Reading abilities in Dutch of course. I needed to come twice to complete them. Then a teacher checks your work/answers and advises you a relevant programme: staatsexamen I of II. After this you will be offered either to take some preparation courses or self-study. I've chosen for courses, 4 half-days: 3 days working in a group and 1 day (Thu) each week is an "exam-day" to test your progress. End of March I'll do staatsexamen II, all 4 parts within 2 days.
I hope my information was useful for you.