I have just gotten home from the test and interview. Thank God I passed 19/20, most of the questions were pretty straightforward and some were twisted just to test your language. Again, you need to read the book at least 2 times to pass the test easily. Based on the experience I had today, I can tell that the online tests might not be enough without reading the book, do them as an extra practice.
I waited about half an hour for the interview, the lady was pretty nice, all the questions were just for verification and to test my language ( she didn't ask for language proof!). she kept the passport's stamps translation in my file. She ended with " everything looks fine we, are just waiting for the security check to be done

then you are ready for the Oath".
Good luck to everybody.