code: def test_pool_single_model(create_X_y):
      X, y = create_X_y
      pool = [
          create_base_classifier(return_value=0, return_prob=[0.9, 0.1])
      ]
      ds_tst = BaseDS(pool_classifiers=pool)
      with pytest.raises(ValueError):
          ds_tst.fit(X, y)
  
imports: import unittest.mock
  from unittest.mock import Mock, MagicMock
  import numpy
  import pytest
  from sklearn.exceptions import NotFittedError
  from sklearn.neighbors import KNeighborsClassifier
  from deslib.base import BaseDS
  from deslib.util.dfp import frienemy_pruning_preprocessed
  from .conftest import create_base_classifier
label_desc: Use image node_id 30 for calling a global function with example usage: test_pool_single_model(create_X_y) without return types