They invite people at random - 320 TR guys, FI, TP pilots and ab initios.
First you'll have a group assignment with about 10 of your peers. It's the standard thing; Solve a problem in limited time, and someone has to present the findings. You'll have about 30 min. The scenarios change every time, but they're never very complicated.
Then you'll have the panel exercise. In groups of 3 or 4. They give you a statement, you have to give an argument for or against the statement in 1 minute, and then your peers get to rebuke your argument. At the end, you'll have to give an answer as a group, so don't be afraid to change your answer based on their arguments. Takes about 15 min tops.
The interview is your standard fair competency based interview. Give a time when x y z why AL, why pilot. They also ask tech questions, but they seem to favour procedures. As in, what would you do when the captains dies after take off? Takes about 30-45 min. As always, you'll never know how you did and what they're looking for exactly. All part of the game
It's the standard fair - They're all very nice people and they'll put you at ease.