From talking to some people who give out these interviews, most of those points really don't matter at all. What matters is A) getting a correct solution and B) being able to explain how you arrived at the solution. Tests, idiomatic code, clean design, etc are not expected and will inevitably waste precious time. Besides, the very nature of the interview (using a walled-off in-browser pseudo-IDE) restricts you from actually writing best-practice code.