code: def test_model_key(self) -> None:
      ms = ModelSpec(model_enum=Models.GPEI)
      self.assertEqual(ms.model_key, "GPEI")
  
imports: import warnings
  from unittest import mock
  from unittest.mock import MagicMock, Mock, patch
  from ax.core.observation import ObservationFeatures
  from ax.exceptions.core import UserInputError
  from ax.modelbridge.factory import get_sobol
  from ax.modelbridge.model_spec import FactoryFunctionModelSpec, ModelSpec
  from ax.modelbridge.modelbridge_utils import extract_search_space_digest
  from ax.modelbridge.registry import Models
  from ax.utils.common.testutils import TestCase
  from ax.utils.testing.core_stubs import get_branin_experiment
  from ax.utils.testing.mock import fast_botorch_optimize
label_desc: Use image node_id 3 for calling the ModelSpecTest obj's underlying member method code with example usage: obj.test_model_key() without return types