I went about 2 weeks ago for the tests. Its all very relaxed however I would give the same advice that I saw on another post be really aware of the time. Many of the tests start off with more difficult questions mixed in early on making it easy to waste too much time.
The morning involved 4 tests plus the personality questionnaire.
There were mathematical, spatial and mechanical reasoning tests.
Maths covered basic algebra, multiplying & dividing fractions and decimals, plus long division and multiplication (these questions often have the answer but have a letter substituted instead of one of the numbers, ie. P7 x P74=7398 what does P=? answer P=2). Multiple choice and plenty of easy ones mixed in.
Spatial test showed flattened plan of a cube with patterns on certain sides of the box. The answers showed various 3d images of the box and you had to work out which was possible. (I hope that makes sense). Started off quite easy but soon changes to non cuboids and some are quite difficult to get your head around. Not sure how you could practice this but just keep an eye on the time (about 60 questions in 25 mins I think). Most of them are fairly straightforward though.
Mechanical test is the usual - if you turn cog A clockwise which way will cog C turn? Which shelf is strongest?(one picture with hinge to middle of shelf other showing hinge to far edge of shelf). Which ball will travel furthest? (one ball thrown straight the other thrown in an arc) that sort of question with lots of nice pictures. All are fairly logical and easy to work out.
Hope that helps and Good luck.
Ps - anyone have any tips for the interview?