code: def test_constructor_preprocessing_step(self):
      preprocessing_params = {}
      ps = Preprocessing(preprocessing_params)
  
      self.assertTrue(len(ps._missing_values) == 0)
      self.assertTrue(len(ps._categorical) == 0)
      self.assertTrue(ps._categorical_y is None)
  
imports: import json
  import copy
  import unittest
  import tempfile
  import numpy
  import pandas
  import uuid
  from supervised.preprocessing.preprocessing_missing import PreprocessingMissingValues
  from supervised.preprocessing.preprocessing_categorical import PreprocessingCategorical
  from supervised.preprocessing.preprocessing import Preprocessing
label_desc: Use image node_id 1 for calling the PreprocessingTest obj's underlying member method code with example usage: obj.test_constructor_preprocessing_step() without return types