[boost] Preferred way to simulate system calls

I like to test every branch, and I have a class that calls open/read/close. It uses a hardcoded filename ("/dev/urandom"). It is a template in a detail namespace. What's the "boost way" when it comes to mocking these system calls? Should I make protected methods that normally call open/read/close, then subclass in a test and override them with different logic to force error paths? - Jim