code: def on_hyperopt_start(self, *args, **kwargs):
      assert self.preprocessed
  
imports: import os.path
  import shutil
  import uuid
  from unittest.mock import patch
  import pytest
  from ludwig.api import LudwigModel
  from ludwig.callbacks import Callback
  from ludwig.constants import ACCURACY, AUTO, BATCH_SIZE, EXECUTOR, MAX_CONCURRENT_TRIALS, TRAINER
  from ludwig.globals import HYPEROPT_STATISTICS_FILE_NAME
  from ludwig.hyperopt.results import HyperoptResults
  from ludwig.hyperopt.run import hyperopt
  from ludwig.hyperopt.utils import update_hyperopt_params_with_defaults
  from ludwig.schema.model_config import ModelConfig
  from tests.integration_tests.utils import binary_feature, create_data_set_to_use, generate_data, number_feature
label_desc: Use image node_id 3 for calling the CustomTestCallback obj's underlying member method code with example usage: obj.on_hyperopt_start() without return types