Many years ago now I had an interview with CAA SRG (which I think is where the job you're going for is based) and there were a bunch of tests beforehand. From what I recall they ranged from some straightforward psychometric stuff and some written exam paper-style sheets related to English comprehension, analysis of data and what conclusions could be drawn from these data and report writing along with a few technical questions to answer specific to the technical domain associated with the job. The tests ran for the whole morning followed by an interview that lasted something approaching 2 hours.
I think they dropped the tests soon after - I heard that they cost a lot of money and didn't provide that much help in selecting people.
I'm not suggesting you'll be faced with anything similar - just telling you what has happened in the past.
As a generalisation I would suggest that you don't worry about the test. If it's a good test that separates the suitable candidates from the unsuitable and you do okay, you'll go into the interview with having already scored a few points. If you don't do okay you probably won't feel comfortable in the job if you do get it. And if the test doesn't help with the selection - do you really want to work for an organisation that can't even get their recruitment right???
OK, that's a bit tongue-in-cheek - focus on the interview questions and having good/smooth answers. The results of the test will probably not carry that much weight and a good interview will score far more points with the technical people (HR people tend to like tests more).
However you approach it - and whatever you face tomorrow - good luck! And let us know what it was like and how you get on.