code: def assert_keys_are_subset(dict1, dict2):
      
      keys1 = set(dict1.keys())
      keys2 = set(dict2.keys())
      unknown_keys = keys2.difference(keys1)
      assert len(unknown_keys) == 0, 'unknown_keys=%r' % (unknown_keys,)
docs: Example:
          >>> # DISABLE_DOCTEST
          >>> dict1 = {1:1, 2:2, 3:3}
          >>> dict2 = {2:3, 3:3}
          >>> assert_keys_are_subset(dict1, dict2)
          >>> #dict2 = {4:3, 3:3}