First they had a video interview, which was absolutely terrifying, but I somehow passed to be invited to the assessment day.
The assessment day wasn't too bad, you get to see their lovely looking offices, most of the people there are very nice, and overall the tests aren't too bad, although you will have to relearn how to do highschool maths.
Apart from tests, they also have you do three "strength based interviews", which I'm not sure what to think about. Evidently I didn't do well at these, because these were the reason they did not offer me a position. However, they also said I should reapply after improving my interview technique, and for a truly strenght based interview that should not matter.
Two of these interviews were quite like the video interview, in that you are asked a question, you respond, and then you get the next question without a real conversation going on... Every once in a while they asked "why do you say that?".
One of them was different, the person who interviewed me was great and gave me feedback for every question and held a conversation. He seemed to care a lot more.
Ohh one last thing: I didn't wear a tie, just a shirt, and regular smart-casual clothes, because to me it seemed that was appropriate from what I read online. I probably should've just asked, that's on me. However, although they said at first that it doesn't matter, when I remarked I was evidently slightly underdressed (as every other candidate was wearing a tie -.- ... Woops) they still said afterwards, I should've worn a tie... So, what I'm trying to say is: Wear a tie!
