class_docstr: Tests for timeline
code: def setUpClass(cls):
      cls.temp_file = "./timeline_temp"
  
      with env(BLUEFOG_TIMELINE=cls.temp_file):
          bf.init()
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import time
  import threading
  import unittest
  import warnings
  import torch
  import bluefog.torch
  from bluefog.common import topology_util
  from bluefog.common.util import env
label_desc: Use image node_id 2 for calling the TimelineTests obj's underlying member method code with example usage: obj.setUpClass(cls) without return types