Just a point, but I would suggest the reason BA didn't say anything about the extra test might be because they didn't want people to be able to practice for it!
Remember that much of this is about testing basic aptitude, not the ability to cram knowledge prior to a test (though I'm sure that will also come in handy at various stages!) and hence if you knew too much about what was coming up, then it wouldn't necessarily be a true reflection.
From what I can tell about the whole process, it seems that BA are trying to test all aspects of a person's abilities. This means that just being a maths or physics genius won't be enough if you can't actually operate effectively as part of a crew; similarly, being an excellent team player with great hand/eye coordination will be redundant if you are perplexed by some intermediate level mental arithmetic!
BA will know what they are looking for, and all we can do is give it our best and hope that will be enough!