The online test needs preparation, simple mathematics but simple mistakes can be made, doing many samples is recommended and necessary. Did not make it to the next phase but i heard its just basic casing.

you get a brief description of 2 interviewers who will be interviewing you beforehand, it is back to back cases, 45 min each. 10 mins on intro and soft question, 30 mins on case, 5 mins for questions at end. they call you within a day or 2 letting you know you progressed to next round. Next round which is final round is with more senior people, MDPs and Partners. Same structure but instead of being online they fly you into the office.

4 step intervieww process case interviews with equal difficulty going from project lead to partner as interviewer, practise cases online and in person and you will do fine. In my opinion its more the nerves that people fall short on