code: def test_init_with_invalid_estimator(self):
      class MyCustomEstimator(object):
          pass
  
      base_estimator = MyCustomEstimator()
      num_classes = 2
  
      with self.assertRaisesRegex(
          ValueError, "Given classifier template must be a subclass"
      ):
          SklearnClassifierFactory(base_estimator, num_classes)
  
file_path: small-text/tests/unit/small_text/classifiers/test_factories.py
imports: import unittest
  from sklearn.svm import LinearSVC
  from sklearn.multiclass import OneVsRestClassifier
  from sklearn.utils.validation import check_is_fitted, NotFittedError
  from small_text.classifiers.classification import SklearnClassifier
  from small_text.classifiers.factories import SklearnClassifierFactory
  from tests.utils.datasets import random_sklearn_dataset
label_desc: Use image node_id 1 for calling the SklearnClassifierFactoryTest obj's underlying member method code with example usage: obj.test_init_with_invalid_estimator() without return types