code: def test_Imputer(self):
      arr = np.array([1, np.nan, 3, 2])
      s = pdml.ModelSeries(arr)
  
      mod1 = s.pp.Imputer(axis=0)
      s.fit(mod1)
      result = s.transform(mod1)
  
      expected = np.array([1, 2, 3, 2])
  
      self.assertIsInstance(result, pdml.ModelSeries)
      self.assert_numpy_array_almost_equal(result.values, expected)
  
      mod1 = s.pp.Imputer(axis=0)
      result = s.fit_transform(mod1)
  
      self.assertIsInstance(result, pdml.ModelSeries)
      self.assert_numpy_array_almost_equal(result.values, expected)
  
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 16 for calling the TestPreprocessing obj's underlying member method code with example usage: obj.test_Imputer() without return types