Hi,
Just sat the test yesterday myself. Its one test about data checking. They run through the whole test as a practice and then you can keep practicing until you are ready. Its 25 questions long and broke into 5 sections. It's all explained really well on the website so you have nothing to worry about.
I got my results back already and thankfully I have passed. As stated before there are no stage 1 interviews until April now and you won't be able to book one until end of Feb.
Good Luck!