code: def test_acquire_unavailable(ray_start_4_cpus):
      """Test that acquiring resources that are not available returns None.
  
      - Try to acquire
      - Assert this does not work
      - Request resources
      - Wait until ready
      - Acquire
      - Assert this did work
      """
      manager = PlacementGroupResourceManager(update_interval_s=0)
      assert not manager.acquire_resources(REQUEST_2_CPU)
  
      manager.request_resources(REQUEST_2_CPU)
      ray.wait(manager.get_resource_futures(), num_returns=1)
      assert manager.acquire_resources(REQUEST_2_CPU)
  
file_path: ray/python/ray/air/tests/execution/test_resource_manager_placement_group.py
imports: import time
  from collections import Counter
  import pytest
  import ray
  from ray.air.execution.resources.placement_group import PlacementGroupResourceManager
  from ray.air.execution.resources.request import ResourceRequest
label_desc: Use image node_id 6 for calling a global function with example usage: test_acquire_unavailable(ray_start_4_cpus) without return types