The interview lasts most of the day and they fly you out to Geneva for it. It is composed of a panel interview (my panel had 5 people including direct supervisor, technical expert, group & department heads and HR rep). You also have to give a presentation based on a topic given to you in advance. After this, I had a technical competence test (case study based on the type of work the role involved). I then went to lunch with the other candidates and recruiters before finishing the day with a series of smaller interviews with existing members of the team. Which order these elements occurs in just depends on how many other candidates are in your selection board and HR's scheduling - you may start with the test or with another element.