class_docstr: Unit test class for testing scikit-learn converter.
code: def test_conversion_bad_inputs(self):
      # Error on converting an untrained model
      with self.assertRaises(Exception):
          model = Imputer()
          spec = converter.convert(model, "data", "out")
  
      # Check the expected class during conversion.
      with self.assertRaises(Exception):
          from sklearn.linear_model import LinearRegression
  
          model = LinearRegression()
          spec = converter.convert(model, "data", "out")
  
file_path: coremltools/coremltools/test/sklearn_tests/test_categorical_imputer.py
imports: import unittest
  from distutils.version import StrictVersion
  import numpy
  from coremltools._deps import _HAS_SKLEARN, _SKLEARN_VERSION
label_desc: Use image node_id 3 for calling the ImputerTestCase obj's underlying member method code with example usage: obj.test_conversion_bad_inputs() without return types