code: def test_run_on_y_only(self):
      d = {"y": ["a", "b", "a", "b"]}
      df = pd.DataFrame(data=d)
      y_train = df.loc[:, "y"]
  
      preprocessing_params = {
          "target_preprocessing": [
              PreprocessingMissingValues.FILL_NA_MEDIAN,
              PreprocessingCategorical.CONVERT_INTEGER,
          ]
      }
  
      ps = Preprocessing(preprocessing_params)
      _, y_train, _ = ps.fit_and_transform(None, y_train)
  
      self.assertEqual(4, y_train.shape[0])
      self.assertEqual(0, y_train[0])
      self.assertEqual(1, y_train[1])
  
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 8 for calling the PreprocessingTest obj's underlying member method code with example usage: obj.test_run_on_y_only() without return types