code: def _transform_pandas(self, df: pd.DataFrame) -> pd.DataFrame:
      self.inputs.append(df)
      rst = df * self.multiplier
      self.outputs.append(rst)
      return rst
  
imports: import uuid
  from typing import Dict, Optional, Union
  from unittest import mock
  import numpy
  import pandas
  import pytest
  import ray
  from ray.air.constants import TENSOR_COLUMN_NAME
  from ray.air.util.data_batch_conversion import BatchFormat
  from ray.data import Preprocessor
  from ray.train._internal.framework_checkpoint import FrameworkCheckpoint
  from ray.train.predictor import Predictor, PredictorNotSerializableException
  from ray.train.tests.util import create_dict_checkpoint, load_dict_checkpoint
label_desc: Use image node_id 3 for calling the DummyPreprocessor obj's underlying member method code with example usage: obj._transform_pandas(df) and returns: rst