code: def test_plot_classification_n_classes():
      X, y = make_blobs()
      X = pd.DataFrame(X)
      X["target"] = 0
      with pytest.raises(ValueError, match="Less than two classes"):
          plot_classification_categorical(X, target_col="target")
      with pytest.raises(ValueError, match="Less than two classes"):
          plot_classification_continuous(X, target_col="target")
  
imports: import pytest
  import numpy
  import pandas
  import matplotlib.pyplot
  import warnings
  import itertools
  from sklearn.datasets import make_regression, make_blobs, load_digits, fetch_openml, load_diabetes
  from sklearn.preprocessing import KBinsDiscretizer
  from dabl.preprocessing import clean, detect_types, guess_ordinal
  from dabl.plot.supervised import plot, plot_classification_categorical, plot_classification_continuous, plot_regression_categorical, plot_regression_continuous
  from dabl.utils import data_df_from_bunch
  from dabl import set_config
label_desc: Use image node_id 4 for calling a global function with example usage: test_plot_classification_n_classes() without return types