code: def test_rabit_tracker():
      tracker = RabitTracker(host_ip="127.0.0.1", n_workers=1)
      tracker.start(1)
      with xgb.collective.CommunicatorContext(**tracker.worker_envs()):
          ret = xgb.collective.broadcast("test1234", 0)
          assert str(ret) == "test1234"
  
file_path: xgboost/tests/python/test_tracker.py
imports: import re
  import sys
  import numpy
  import pytest
  import xgboost
  from xgboost import RabitTracker, collective
  from xgboost import testing
label_desc: Use image node_id 1 for calling a global function with example usage: test_rabit_tracker() without return types