code: def test_update_unknown_flag(self):
      with self.assertRaisesRegex(
          LookupError, "Unrecognized config option"
      ):
          config.update("unknown", True)
  
file_path: flax/tests/configurations_test.py
imports: from unittest import mock
  from absl.testing import absltest
  from flax.configurations import bool_flag, config
label_desc: Use image node_id 6 for calling the MyTestCase obj's underlying member method code with example usage: obj.test_update_unknown_flag() without return types