code: def test_objectmapper(self):
      df = pdml.ModelFrame([])
      self.assertIs(df.preprocessing.Binarizer, pp.Binarizer)
      self.assertIs(
          df.preprocessing.FunctionTransformer, pp.FunctionTransformer
      )
      self.assertIs(df.preprocessing.Imputer, pp.Imputer)
      self.assertIs(df.preprocessing.KernelCenterer, pp.KernelCenterer)
      self.assertIs(df.preprocessing.LabelBinarizer, pp.LabelBinarizer)
      self.assertIs(df.preprocessing.LabelEncoder, pp.LabelEncoder)
      self.assertIs(
          df.preprocessing.MultiLabelBinarizer, pp.MultiLabelBinarizer
      )
      self.assertIs(df.preprocessing.MaxAbsScaler, pp.MaxAbsScaler)
      self.assertIs(df.preprocessing.MinMaxScaler, pp.MinMaxScaler)
      self.assertIs(df.preprocessing.Normalizer, pp.Normalizer)
      self.assertIs(df.preprocessing.OneHotEncoder, pp.OneHotEncoder)
      self.assertIs(
          df.preprocessing.PolynomialFeatures, pp.PolynomialFeatures
      )
      self.assertIs(df.preprocessing.RobustScaler, pp.RobustScaler)
      self.assertIs(df.preprocessing.StandardScaler, pp.StandardScaler)
  
imports: import pytest
  import numpy
  import pandas
  import sklearn.datasets
  import sklearn.preprocessing
  import pandas_ml
  import pandas_ml.util.testing
label_desc: Use image node_id 1 for calling the TestPreprocessing obj's underlying member method code with example usage: obj.test_objectmapper() without return types