code: def cpu_fallback_warning(self):
      with self.assertWarnsRegex(
          UserWarning, "No GPU/TPU found, falling back to CPU"
      ):
          xb.get_backend()
  
imports: import os
  import platform
  import time
  import warnings
  from absl import logging
  from absl.testing import absltest
  from jax._src import compiler
  from jax._src import config
  from jax._src import test_util
  from jax._src import xla_bridge
  from jax._src.interpreters import xla
  from jax._src.lib import xla_client
label_desc: Use image node_id 13 for calling the GetBackendTest obj's underlying member method code with example usage: obj.cpu_fallback_warning() without return types