code: def test_list_in_list(self):
      callback = "test"
      clist = CallbackList([callback])
      clist2 = CallbackList([clist])
      self.assertTrue(clist2.callback_list[0] == "test")
  
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 5 for calling the TestCallbackList obj's underlying member method code with example usage: obj.test_list_in_list() without return types