I got in with ACL earlier this year but turned down the offer. However the day consisted of the following:
Maths Test.
Spelling Test.
Interview with HR.
Interview with Chief and another Senior Pilot.
Maths was a bit tricky - spelling test was easy. Interviews were fairly straighforward - I wasn't asked anything technical on the ATR - just more about why do I want to join and your flying career to date.
They were a decent bunch and I know that your are well looked after once you're in.