Heyy, I'm currently in year 11 at JMSS and I'd be happy to help anyone who wants some!
Here's some basic info on the tests, all subject to change obviously.
The test was composed of 2 prac/scientific report write ups, 2 mathematical tests and a scientific reasoning test I believe (it's been so long now but I think thats it).
In order to do your best on the write ups you should have as strong a knowledge as possible of years 8-9 science, though one of the options for my prac writeup was year 6 content! My topics for the first one were something along the lines of explaining an sense and how animals have adapted to use it or writing up a separation of sand, salt, water and iron filaments. My second write up was to create a plan for a museum exhibition about senses (for some reason the topics were quite similar, don't expect this every year!) and it was a little more creative than the other one (I even drew a little diagram of a bat with my extra time).
For the mathematics test I'd highly recommend going through your year 9 textbook/asking your teacher for a yearly plan as you'll want to have a basic knowledge of year 9 mathematics the whole way through. Surds, factorising and also lots of fraction questions were the most common topics in the first test in my experience, but it really is from the whole of year 9 mathematics. The numerical reasoning is basically just number patterns and things like that, if you can I'd recommend doing the Edutest ones because that seems to be the only thing that is really consistent with the practice tests and the actual test.
Surprisingly, the scientific reasoning test was probably the easiest (imo) as it was basically just applying simple scientific concepts to situations and interpreting data. For example, one of my questions had an illustration of a string of nucleotides, the corresponding code and was essentially 'T represents Thymine, U represents Uracil, what would be the outcome if all Thymine were replaced with Uracils' and the options were for example 'UCTAUUAT', 'GUTAGGAT' and 'GCUAGGAU'.
If you have anymore questions let me know!