code: def test_placement_group(ray_start_2_cpus):
      """Tests that workers can be removed and added to a placement group."""
      num_workers = 2
      bundle = {"CPU": 1}
      bundles = [bundle.copy() for _ in range(num_workers)]
      placement_group = ray.util.placement_group(bundles)
      wg = WorkerGroup(
          num_workers=num_workers, placement_group=placement_group
      )
      wg.remove_workers([0])
      wg.add_workers(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 17 for calling a global function with example usage: test_placement_group(ray_start_2_cpus) without return types