new_contents: # test containment operator on subclass of a native type
  
  class mylist(list):
      pass
  
  class mydict(dict):
      pass
  
  class mybytes(bytes):
      pass
  
  l = mylist([1, 2, 3])
  print(0 in l)
  print(1 in l)
  
  d = mydict({1:1, 2:2})
  print(0 in l)
  print(1 in l)
  
  b = mybytes(b'1234')
  print(0 in b)
  print(b'1' in b)
  
subject: Add test for containment of a subclass of a native type.