I tell them to do it in any language they're comfortable with, though obviously, if they're interviewing for a Ruby rule, I'd be surprised if they didn't do it

I tell them to do it in any language they're comfortable with, though obviously, if they're interviewing for a Ruby rule, I'd be surprised if they didn't do it in Ruby. I actually do ask them to write the code - I'd expect most programmers to know the basic syntax of the language the claim to be proficient in, but I've seen Ruby developers who are unable to correctly use Array#each, which would be a red flag.