code: def step(self):
      return {"iter": self.training_iteration}
  
imports: import json
  import os
  from typing import Dict, Union
  import pytest
  import ray
  from ray import train, tune
  from ray.train._internal.storage import StorageContext
  from ray.tune.trainable import wrap_function
  from ray.train.tests.util import create_dict_checkpoint
label_desc: Use image node_id 2 for calling the SavingTrainable obj's underlying member method code with example usage: obj.step() and returns: dict