IMO if you're giving people 'gotcha' programming tests in an interview, then you don't know how to select candidates or interview in the first place.
You should be looking for competence by looking at their programming accomplishments, both in and out of work, as well as their ability and desire to teach themselves (probably the most important trait IMO).
I disagree. IMO asking someone whether they can program a loop that demonstrates the use of a mod operator is a 'gotcha' test because it proves nothing as far as their suitability as programmer and as an employee and is designed soley to weed people out based on one thing. Sure, maybe they are completely ignorant... or maybe they were just nervous that day or unfamiliar with a particular language's mod operator. Lots of programmers don't do well in high-pressure situations... which incidentally programming is not most of the time.
How about asking someone how they got interested in programming, or what sort of things they've created with their knowledge in and out of work, or what languages/technologies they've taught themselves in their free time, how they go about fixing puzzling software problems, or what they consider to be good vs. bad programming practices, or even what their hobbies are? - those kinds of things that will tell you IMO whether they are smart, passionate, and will make a good employee.
> unfamiliar with a particular language's mod operator
Just anecdotally, over some hundred interviews, I've never ever ran into a candidate who failed one of these FizzBuzz style loop writing tests because the didn't know the mod operator, or were nervous enough not to remember it.
I see a lot of candidates that can't remember what params some standard system call is supposed to take and I always tell them I'm happy as long as they define what they think it looks like. Heck, most of the time I have no clue myself.
I'm not claiming the candidate you describe (competent but can't remember a for loop) doesn't exist, just that I've never personally encountered such a beast. Quite the contrary, with a technically open minded interviewer it seems hard to get even the most introvert candidate to stop talking shop .. :-)
You should be looking for competence by looking at their programming accomplishments, both in and out of work, as well as their ability and desire to teach themselves (probably the most important trait IMO).