Big Playa - re-read the requirements… you failed.
I ask the candidate to write a simple but full-fledge class from scratch. (Many can’t)
I also provide a series of assertions and ask the candidate to write code that passes those tests.
However, writing code on a whiteboard is hard even for me, and I’ve written a lot of code in the last 20 years. These days I’d provide the candidate with a laptop (if they don’t have one with them) and watch them code and test their code.