code: def test_define_holdout_set_str(monkeypatch):
      dummy_df = pd.DataFrame(dict(a=[0, 1], b=[2, 3]))
  
      # noinspection PyUnusedLocal
      def mock_pandas_read_csv(*args, **kwargs):
          return dummy_df
  
      monkeypatch.setattr(pd, "read_csv", mock_pandas_read_csv)
      assert define_holdout_set(
          pd.DataFrame(dict(a=[4], b=[5])), "foo", "x"
      )[1].equals(dummy_df)
  
imports: from hyperparameter_hunter.callbacks.recipes import confusion_matrix_oof, confusion_matrix_holdout
  from hyperparameter_hunter.environment import Environment, define_holdout_set, validate_file_blacklist
  import numpy
  import pandas
  from pkg_resources import get_distribution
  import pytest
  from sklearn.datasets import load_breast_cancer
  from sklearn.metrics import accuracy_score
  from sklearn.model_selection import RepeatedStratifiedKFold
label_desc: Use image node_id 14 for calling a global function with example usage: test_define_holdout_set_str(monkeypatch) and returns: dummy_df