class_docstr: Test FeatureImportances visualizer
docstr: Raises an exception when classes param not found
docstr_tok: ["Raises","an","exception","when","classes","param","not","found"]
code: def test_find_classes_param_not_found(self):
      """
      Raises an exception when classes param not found
      """
      model = MockClassifier()
      visualizer = FeatureImportances(model)
  
      assert not hasattr(model, "classes_")
  
      e = "could not find classes_ param on {}".format(
          visualizer.estimator.__class__.__name__
      )
      with pytest.raises(YellowbrickTypeError, match=e):
          visualizer._find_classes_param()
  
imports: import pytest
  import numpy
  import numpy.testing
  import matplotlib.pyplot
  from yellowbrick.exceptions import NotFitted
  from yellowbrick.model_selection.importances import *
  from yellowbrick.datasets import load_occupancy, load_concrete
  from sklearn.datasets import load_iris
  from sklearn.ensemble import RandomForestClassifier
  from sklearn.ensemble import GradientBoostingClassifier
  from sklearn.base import BaseEstimator, ClassifierMixin
  from sklearn.linear_model import LogisticRegression, Lasso
  from sklearn.impute import SimpleImputer
  from sklearn.pipeline import Pipeline
  from unittest import mock
  from tests.base import VisualTestCase
label_desc: Use image node_id 19 for calling the TestFeatureImportancesVisualizer obj's underlying member method code with example usage: obj.test_find_classes_param_not_found() without return types