I believe that all methods should act the same, but they don't as a result of the work done in issue12170.  E.g. find will accept integer input but split will not.  Given this comment at the top of test_bytes.py "XXX This is a mess.  Common tests should be moved to buffer_tests.py, which itself ought to be unified with string_tests.py (and the latter should be modernized).", it looks like a thorough review of the code and tests is in order.