docstr: Test the step_based_gs_only decorator
code: def test_step_based_gs_only(self) -> None:
      """Test the step_based_gs_only decorator"""
      sobol_model_spec = ModelSpec(
          model_enum=Models.SOBOL,
          model_kwargs={},
          model_gen_kwargs={"n": 2},
      )
      gs_test = GenerationStrategy(
          nodes=[
              GenerationNode(
                  node_name="node_1",
                  model_specs=[sobol_model_spec],
              ),
              GenerationNode(
                  node_name="node_2",
                  model_specs=[sobol_model_spec],
              ),
          ],
      )
      with self.assertRaisesRegex(
          UnsupportedError, "is not supported for GenerationNode based"
      ):
          gs_test.current_step_index
  
imports: import logging
  from typing import cast, List
  from unittest import mock
  from unittest.mock import MagicMock, patch
  from ax.core.arm import Arm
  from ax.core.base_trial import TrialStatus
  from ax.core.experiment import Experiment
  from ax.core.generator_run import GeneratorRun
  from ax.core.observation import ObservationFeatures
  from ax.core.parameter import ChoiceParameter, FixedParameter, Parameter, ParameterType
  from ax.core.search_space import SearchSpace
  from ax.core.utils import get_pending_observation_features_based_on_trial_status
  from ax.exceptions.core import DataRequiredError, UnsupportedError, UserInputError
  from ax.exceptions.generation_strategy import GenerationStrategyCompleted, GenerationStrategyMisconfiguredException, GenerationStrategyRepeatedPoints, MaxParallelismReachedException
  from ax.modelbridge.discrete import DiscreteModelBridge
  from ax.modelbridge.factory import get_sobol
  from ax.modelbridge.generation_node import GenerationNode
  from ax.modelbridge.generation_strategy import GenerationStep, GenerationStrategy
  from ax.modelbridge.model_spec import ModelSpec
  from ax.modelbridge.random import RandomModelBridge
  from ax.modelbridge.registry import Cont_X_trans, MODEL_KEY_TO_MODEL_SETUP, Models
  from ax.modelbridge.torch import TorchModelBridge
  from ax.modelbridge.transition_criterion import MaxGenerationParallelism, MaxTrials, MinTrials
  from ax.models.random.sobol import SobolGenerator
  from ax.utils.common.equality import same_elements
  from ax.utils.common.mock import mock_patch_method_original
  from ax.utils.common.testutils import TestCase
  from ax.utils.common.typeutils import not_none
  from ax.utils.testing.core_stubs import get_branin_data, get_branin_experiment, get_choice_parameter, get_data, get_experiment_with_multi_objective, get_hierarchical_search_space_experiment
label_desc: Use image node_id 30 for calling the TestGenerationStrategy obj's underlying member method code with example usage: obj.test_step_based_gs_only() without return types