I had to take an aptitude and personality test. Once I passed that, the interview was brief and the job was offered to me mostly based on my college degree and the fact that I had previously managed people at another company. One of the most important pieces in my understanding is the personality portion of the interview though, because you often have to deal with difficult people on the job and have to interact well with both union and non union employees.

They only hire from within. The interview process is more about you understanding the actual role and commitment of the job. If you're picked for a part time supervisor interview, you already got the job.