During all the interviews, the interviewers started with the basic background questions, but then eventually evolved into a series of "test" questions (which mostly seemed prepared in advanced). These were used to get an idea of your overall "thinking skill" - not specific to the job. They were stories that required reasoning and not jumping to the first answer that comes to mind. Overall, they appear to test you general logical reasoning skills/intelligence. The interviewers also typed all of my answers as I spoke. I suppose this is to record my responses in a database so that if I ever apply for a job again at Google, the new interviewers can see my prior responses.