That's true, however asking someone on the spot to write a function that requires domain specific knowledge isn't a good solution. What are you in fact testing, do they know how to code or do they know how to calculate the area of a circle. I can code but I'd fail horribly on the area of the circle thing simply because I haven't done anything like that since grade school math class probably 30 years ago.

So his comment is valid in that coders should code but his example of how to tell if someone can code I think is flawed.