class_docstr: Tests for timeline
code: def test_timeline_with_python_interface(self):
      bf.timeline_start_activity(
          "test_python_interface_x", "FAKE_ACTIVITY"
      )
      time.sleep(0.1)
      bf.timeline_end_activity("test_python_interface_x")
      time.sleep(0.1)
  
      file_name = f"{self.temp_file}{bf.rank()}.json"
      with open(file_name, "r") as tf:
          timeline_text = tf.read()
          assert "FAKE_ACTIVITY" in timeline_text, timeline_text
  
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 6 for calling the TimelineTests obj's underlying member method code with example usage: obj.test_timeline_with_python_interface() without return types