Hi mate, i did this test a few years ago, i did pass but i decided not to proceed as i got offered something elsewhere, i wouldn't worry to much provided you are clued up on the basics.
From what i remember there was an english reading test, basically you read a paragraph and then have to choose what statement is true from the paragraph, a lot of it is based on Airbus and health and safety! There was also a test which tested your understanding of a paragraph, for example there would be a partial sentence and you would then select from four choices which part would make sense to finish it.
There was a maths test which was basic GCSE maths, such as percentages, division etc, very easy, you can use a calculator from what i remember so don't forget one. I remember also there were quite a few questions like if you had X amount of passengers on a plane, paying this amount, how much does it cost per seat and it then expands into VAT and stuff like that. It isn't hard if your fine at GCSE level maths.
Technical understanding i can't remember to much but i do remember one or two just asked what a certain action on something would do. For example you would be presented with several gears in sequence and the question would ask if gear 1 turned in this direction, which direction would gear 3 go in etc. This is pretty impossible to revise but i wouldn't worry to much.
Hope this helps,
Good luck!