code: def check(self, diff):
      diff = list(diff)  # trigger exceptions first
      for line in diff:
          self.assertIsInstance(
              line,
              bytes,
              "all lines of diff should be bytes, but got: %r" % line,
          )
  
imports: import difflib
  from test.support import findfile
  import unittest
  import doctest
  import sys
label_desc: Use image node_id 1 for calling the TestBytes obj's underlying member method code with example usage: obj.check(diff) without return types