Redbubble is not unique in expecting interview candidates to be able to analyze and design a model for a complicated problem on the fly. It’s a useful and interesting mental exercise for developers, and it gives us an amazing insight into how candidates go about solving problems. But it can also be stressful for candidates who aren’t used to it. The interview will begin like this: We will give you some ‘business rules’ for a system we would like designed, maybe also a few constraints, and then we will ask you to design it for us. The final design you come up with will be different for every problem-person combination, so I can’t tell you what the answer will be.