you'll get the standard tech exam (basically stuff from the ATP written) another test that's basically a personality profile test, and the interview.
there'll be a HR person and a captain. you'll get the standard "tell us about yourself," "why do you want to work here," and "tell me about...," questions from the HR person. the Capt. will ask a couple system questions about the last AC you flew, or as you toe explain the system if it's a nAC they aren't familiar with.
then if you're prior 121, you're done. everybody else gets a sim ride, which i know nothing about (former 121)
be confident about yourself, and have a good handle on your knowledge. you'll have to put an effort in to not get the job