class_docstr: Test FeatureImportances visualizer
docstr: Test identification if is fitted
docstr_tok: ["Test","identification","if","is","fitted"]
code: def test_is_fitted(self):
      """
      Test identification if is fitted
      """
      visualizer = FeatureImportances(Lasso())
      assert not visualizer._is_fitted()
  
      visualizer.features_ = "foo"
      assert not visualizer._is_fitted()
  
      visualizer.feature_importances_ = "bar"
      assert visualizer._is_fitted()
  
      del visualizer.features_
      assert not visualizer._is_fitted()
  
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 21 for calling the TestFeatureImportancesVisualizer obj's underlying member method code with example usage: obj.test_is_fitted() without return types