I think you'll find the assessment day well structured and very fair. The tests are all computer based and consist of;
1. A general knowledge test about anything from music to history or science
2. Maths tests
3. Aeronautical knowledge test
4. B777 tech questionnaire
5. English Language test for non-native speakers
6. Various Puzzle tests - IQ type things
7. Psychometric profile test
The simulator test was conducted in a 737NG sim; it's all raw data flying, taking off from 26L LEJ to do some steep turns, climbing and leveling off in the turn, descending and leveling off in the turn, followed by an engine failure then SE NDB and missed approach then ILS to land.
Good luck; I think it'll be a great job if you can make the grade, so pm me if you need any further information.