The interview process is very relaxed. I made a point to dress nicely out of respect, and I would always recommend doing so, but everyone involved in the interviewing process is friendly and fairly casual. Expect some serious, thought-provoking questions alongside a friendly exchange of humor. Be ready to talk.
There were two interviews for me. The first interview consisted of a basic skills test and a good conversation. The second interview consisted of another good conversation. I enjoyed the interview process.