I'm kinda late but oh well :')
The tests were actually pretty easy. For anyone trying out next year, you don't really have to go overboard with studying a lot of scientific content. Just try the practice tests and understand most of the Year 9 and 8 maths topics.
For the prac, you just needed to write a discussion and answer the questions given to you. The scientific essay took me by surprise XD Was not expecting it at all. But there has been a trend with environmental topics when it comes to essays, so I dunno. Just something to look out for.
I would recommend you to practise writing essays. My tutor suggested me to do GAT (General Achievement Test), and pick a topic that involves science. I suggest you to do the 2013 and 2016 as they contain scientific contents. In writing (essay, not the prac), it states the topic, and it also provides some information that you should include in your writing (I don't think that I did well for it because I struggled to write intro and linking sentences for each body paragraph (TEEL). Idk if we do the TEEL structure because it wasn't a persuasive nor discussion, but it was a report). Also, for the math and numerical reasoning tests, they also cover year 10. When we did these two tests, they pretty much had the same type of questions as in the selective high school exam.
For those who went for the selective high school, the JMSS test was easier than the selective one. idk if it has happened to you guys, but after I finished the exam, I wasn't tired at all, and idk why, lol.