The application process for me (Germany) was: 1) online application, 2) online assessment, 3) recruitment day. The online test assesses verbal, numeric and analytical skills. I didn’t prepare for that, it was quite simple. On the recruitment day you have to solve a case study with other candidates and then present the results. I prepared extensively for normal case studies and personal fit questions like for the other interviews I had, so I didnt really focus on group cases. It was a bit difficult for me on the assessment day as I felt mentally unprepared for the situation. I don't know which location you are applying for but hope this is still helpful info.