Diveplane interview questions

There is an initial Interview with HR followed by a assessment where you write a python application for them. The application will take at least a few hours to do. I was turned down after submitting the application with no feedback on what was wrong with it. Best case, they don't care about your time. Worst case, they are using their interviewees for free labor. If someone spends hours working on an unpaid project then you should at least leave constructive criticism.