It mostly is language specific though isn't it? Take python: IOError is a global, one main way to print, you don't have to worry about the output buffer.
So, for example, if you are in Python3, sys.in and sys.out are by default in text mode, which is not going to end well for anyone.
It's a trivial test, so I'll give you trivial input and not have you worry about "what if someone gives me random bytes".
The test isn't to demonstrate you know off the top of your head how to deal with an edge case. But if it were and I were allowed to pick my language, I'd pick bash and just write
catThe only edge case is knowing you need to flush the output, which is relevant whether you send ASCII text or not. The other edge cases around ASCII are just whether you use the correct API's or not.