code: def test_for_list(self):
      self.list.on_start({})
      self.assertTrue(self.callback_1.method_calls[0][0] == "on_start")
      self.assertTrue(self.callback_2.method_calls[0][0] == "on_start")
  
file_path: torchbearer/tests/callbacks/test_callbacks.py
imports: import warnings
  from unittest import TestCase
  from mock import MagicMock, Mock
  import torchbearer
  from torchbearer.callbacks import CallbackList, Tqdm, TensorBoard
label_desc: Use image node_id 4 for calling the TestCallbackList obj's underlying member method code with example usage: obj.test_for_list() without return types