Ask HN: Minimalist Coding Challenge Tool?

I'm trying to setup a super-minimal coding challenge I can invite candidates to: complete this function in ruby, complete this other function in javascript. Under 30 min.

The platform runs the submissions against my tests, and if they pass, I'll review the actual code.

Everything I'm seeing wants to subject candidates to 2hr screenings for a bunch of skills with plagiarism detection and what all, and I just want to give them a quirky little challenge to show that they know what they're doing and have taste.

Any suggestions?