class_docstr: Unit test class for testing scikit-learn converter.
code: def test_conversion(self):
      spec = converter.convert(
          self.scikit_model, "data", "out"
      ).get_spec()
      self.assertIsNotNone(spec)
  
      # Test the model class
      self.assertIsNotNone(spec.description)
  
      # Test the interface
      self.assertTrue(spec.pipeline.models[-1].HasField("imputer"))
  
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 2 for calling the ImputerTestCase obj's underlying member method code with example usage: obj.test_conversion() without return types