code: def on_shutdown(
      self, worker_group: WorkerGroup, backend_config: TestConfig
  ):
      pass
  
imports: import logging
  import pytest
  import ray
  from ray import train, tune
  from ray.air.constants import TRAINING_ITERATION
  from ray.train import FailureConfig, RunConfig, ScalingConfig
  from ray.train._internal.worker_group import WorkerGroup
  from ray.train.backend import Backend, BackendConfig
  from ray.train.data_parallel_trainer import DataParallelTrainer
  from ray.train.examples.pytorch.torch_fashion_mnist_example import train_func_per_worker
  from ray.train.examples.tf.tensorflow_mnist_example import train_func
  from ray.train.tensorflow.tensorflow_trainer import TensorflowTrainer
  from ray.train.tests.util import create_dict_checkpoint, load_dict_checkpoint
  from ray.train.torch.torch_trainer import TorchTrainer
  from ray.tune.tune_config import TuneConfig
  from ray.tune.tuner import Tuner
label_desc: Use image node_id 2 for calling the TestBackend obj's underlying member method code with example usage: obj.on_shutdown(worker_group, backend_config) without return types