Bens correct, it's uncommon to say 'sit for a test' in the US. 'Take a test' would be a better option.

I have never heard "to sit for a test". I have always heard "to take a test".

I've heard 'sit for' used in conjunction with professional licensing exams here in the US. Example: He sat for the bar exam. { A bar exam is required in order to become licensed as a lawyer in the United States. } Example: My sister sat for her CPA { Certified Public Account } in 1979.