code: def test_unknown_backend_error(self):
      with self.assertRaisesRegex(RuntimeError, "Unknown backend foo"):
          xb.get_backend("foo")
  
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 9 for calling the GetBackendTest obj's underlying member method code with example usage: obj.test_unknown_backend_error() without return types