I've interviewed several hundred people and gave them a take home test of a simple problem that we had encountered in our work. We asked them to write a simple

I've interviewed several hundred people and gave them a take home test of a simple problem that we had encountered in our work. We asked them to write a simple API that would return the closest pharmacy, given a latitude and longitude supplied to the API, and gave them a CSV with 10 pharmacies. Language didn't matter, and we never even ran it to see if it actually worked. During the interview we would have them walk us through the code and explain what each part does and why they did whatever (this makes sure they actually wrote it and understand it). Then, we would throw curveballs like "what would you need to change in your code if there were 100,000 pharmacies", and "how would you need to change it to return the closest 10 pharmacies instead of the closest 1?" It's normally really difficult to get into someone's head about HOW they solve problems. I really felt like our method shined a light on their programming abilities. Also, how well they might anticipate future usage by building something smart to begin with and not code themselves into a corner.