code: def test_multiple_fallback(self):
      global_m = C._dispatch_library("IMPL", "_", "XLA")
      global_m.fallback_fallthrough(),
      try:
          global_m.fallback_fallthrough(),
      except RuntimeError as e:
          self.assertExpectedInline(
              str(e),
              """Tried to register multiple backend fallbacks for the same dispatch key XLA; previous registration """
              """registered at /dev/null:0, new registration registered at /dev/null:0""",
          )
      else:
          self.assertTrue(False)
  
imports: import torch._C
  from torch.testing._internal.common_utils import TestCase, run_tests
  from torch._python_dispatcher import PythonDispatcher
  from collections import namedtuple
  import itertools
  import os
  import re
  import torch.utils.cpp_extension
label_desc: Use image node_id 23 for calling the TestDispatch obj's underlying member method code with example usage: obj.test_multiple_fallback() without return types