code: def test_execute_single(ray_start_2_cpus):
      wg = WorkerGroup(num_workers=2)
  
      def f():
          import os
  
          os.environ["TEST"] = "1"
  
      wg.execute_single(1, f)
  
      def check():
          import os
  
          return os.environ.get("TEST", "0")
  
      assert wg.execute(check) == ["0", "1"]
  
imports: import time
  from collections import defaultdict
  import pytest
  import ray
  import ray._private.ray_constants
  from ray.train._internal.worker_group import Worker, WorkerGroup, WorkerMetadata
label_desc: Use image node_id 15 for calling a global function with example usage: test_execute_single(ray_start_2_cpus) and returns: os