code: def _check_ctx(self, mode, *, mode_nothing_raises=False):
      if mode == "warn":
          return self.assertWarnsRegex(
              UserWarning, "an autograd kernel was not registered"
          )
      assert mode == "nothing"
      if mode_nothing_raises:
          return self.assertRaisesRegex(
              RuntimeError, "does not require grad"
          )
      return contextlib.nullcontext()
  
imports: import contextlib
  import warnings
  import numpy
  import torch
  from torch.library import Library
  from torch.testing._internal.common_utils import instantiate_parametrized_tests, parametrize, run_tests, TestCase
label_desc: Use image node_id 6 for calling the TestAutogradFallback obj's underlying member method code with example usage: obj._check_ctx(mode) and returns: contextlib, self, self