I did it two years ago, not sure how much had changed since, they seem to like playing with the recruitment process a bit, I know the pre-assessment day tests have been altered.
There will be a group chat outlining the day at the beginning, then break off and have the interviews. At some point there will be an ishihara colour blindness test, and certificates and eligibility to work documents copied. There's also the group exercise, which for me was contacting something to a specific spec for a certain task out of paper and other stationary. It's not completing the task that's important so much as showing leadership skills.
Also, it might say parents can attend, but none do, or at least never did the three batches of people I've seen have the assessments.