code: def test_plot_pd_variance_targets_unknown(exp_importance):
      """Test if an error is raised when the ``targets`` contains an unknown values."""
      with pytest.raises(ValueError) as err:
          plot_pd_variance(exp=exp_importance, targets=["unknown"])
      assert "Unknown `target` name." in str(err.value)
  
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 30 for calling a global function with example usage: test_plot_pd_variance_targets_unknown(exp_importance) without return types