code: def test_plot_pi_metric_name_unknown(exp):
      """Test if an error is raised when the metric name is unknown."""
      metric_name = "unknown"
      with pytest.raises(ValueError) as err:
          plot_permutation_importance(
              exp=exp, metric_names=[metric_name]
          )
      assert "Unknown metric name." in str(err.value)
  
imports: import re
  from copy import deepcopy
  import matplotlib.pyplot
  import numpy
  import pytest
  from pytest_lazyfixture import lazy_fixture
  from sklearn.metrics import accuracy_score, f1_score, max_error
  from alibi.api.defaults import DEFAULT_DATA_PERMUTATION_IMPORTANCE, DEFAULT_META_PERMUTATION_IMPORTANCE
  from alibi.api.interfaces import Explanation
  from alibi.explainers import PermutationImportance, plot_permutation_importance
label_desc: Use image node_id 21 for calling a global function with example usage: test_plot_pi_metric_name_unknown(exp) without return types