I have not used a site specifically, but when I interview developers, apart from the normal technical questioning on their CV, I get them to design a simple obj

I have not used a site specifically, but when I interview developers, apart from the normal technical questioning on their CV, I get them to design a simple object diagram, and then lead them to a PC. I ask them to code it test first. We observe them doing it to see how comfortable they are with the tools and that they can even complete the code for the design.