You get called into an "assessment centre" to do a group interview. The first part of the interview they gather personal documents, once that is done they start with a power point presentation outlining what will happen during the day. The first thing they do is give you 2 minutes to read over and describe what you would do in a particularly stressful situation, you must give a detailed written answer within a short time space.
second comes the quizzes, you are giving a brief video then asked to answer several multiple choice questions
You're then either take for a 1on1 interview where they ask several "Give me a time when you" questions
Finally there is a group activity, it is designed to be high stress to see how you function with multi tasking under pressure.
The entire process takes 3 - 4 hours with most of that time just sitting and waiting to go into your 1 on 1 interview. The group assessment is a particular stand out as a bad experience as the people you are in a group with are going to determine how well you can stand out as a participant... Ultimately the whole process is somewhat dated and not well run so be aware.