I had just one interview, over Skype as I was in school at the time as was not able to go to their office. It lasted about 15-20 minutes, a few people including the project manager and project lead asked me various questions about my experience and knowledge, how quickly i learn, etc. I answered honestly, I was just about to graduate so I didn't have any full time work experience, but they were impressed with my school experience (soon to be BS in physics) and since I had computer experience as part of my major's required classes, they were impressed enough to hire me.