code: def test_unknown_method(method):
      """Test whether an unknown method raises an error."""
      explainer = PartialDependenceVariance(
          predictor=lambda x: np.random.empty(len(x))
      )
      with pytest.raises(ValueError) as err:
          explainer.explain(X=np.empty((10, 3)), method=method)
      assert re.search("unknown method", err.value.args[0].lower())
  
imports: import re
  from copy import deepcopy
  import matplotlib.pyplot
  import numpy
  import pandas
  import pytest
  from pytest_lazyfixture import lazy_fixture
  from sklearn.ensemble import GradientBoostingRegressor
  from sklearn.linear_model import LinearRegression
  from alibi.api.defaults import DEFAULT_DATA_PDVARIANCE, DEFAULT_META_PDVARIANCE
  from alibi.api.interfaces import Explanation
  from alibi.explainers import PartialDependence, PartialDependenceVariance, TreePartialDependence
  from alibi.explainers.pd_variance import _plot_feature_importance, _plot_feature_interaction, _plot_hbar, plot_pd_variance
label_desc: Use image node_id 3 for calling a global function with example usage: test_unknown_method(method) without return types