code: def on_fold_start(self):
      super().on_fold_start()
  
      self.__assert_about_prediction(
          ["final", "rep"], lambda _: _ is not None
      )
      self.__assert_prediction_is_zero(["fold"])
  
imports: from hyperparameter_hunter import Environment, CVExperiment
  from hyperparameter_hunter.callbacks.bases import BaseCallback
  from hyperparameter_hunter.settings import G
  from hyperparameter_hunter.utils.learning_utils import get_breast_cancer_data
  from copy import deepcopy
  import pandas
  import pytest
  from sklearn.datasets import load_iris
  from sklearn.metrics import f1_score
  from sklearn.model_selection import train_test_split
  from sklearn.preprocessing import LabelEncoder
  from xgboost import XGBClassifier
label_desc: Use image node_id 4 for calling the DummyExperimentPredictorHoldout obj's underlying member method code with example usage: obj.on_fold_start() without return types