As far as I know you only have to take 2 interviews. 1 with the HR person, 1 with the manager in question, which will be your mentor/supervisor. Both are not technical, definitely more exploratory and focused on the candidate. However it doesn't hurt to know about the company in general (what they do, the brands, etc). The HR person in charge of interviewing you is overall very nice, and young, so that put me at ease. Overall, I enjoyed it and it left me with a positive impression of the group.