code: def test_select_ops_ensure_at_least_one_live_operator():
      opt = ExecutionOptions()
      inputs = make_ref_bundles([[x] for x in range(20)])
      o1 = InputDataBuffer(inputs)
      o2 = MapOperator.create(
          make_map_transformer(lambda block: [b * -1 for b in block]),
          o1,
      )
      o3 = MapOperator.create(
          make_map_transformer(lambda block: [b * 2 for b in block]),
          o2,
      )
      topo, _ = build_streaming_topology(o3, opt)
      topo[o2].outqueue.append(make_ref_bundle("dummy1"))
      o1.num_active_tasks = MagicMock(return_value=2)
      assert (
          select_operator_to_run(
              topo,
              TopologyResourceUsage(
                  ExecutionResources(cpu=1), EMPTY_DOWNSTREAM_USAGE
              ),
              ExecutionResources(cpu=1),
              [],
              True,
              "dummy",
              AutoscalingState(),
          )
          is None
      )
      o1.num_active_tasks = MagicMock(return_value=0)
      assert (
          select_operator_to_run(
              topo,
              TopologyResourceUsage(
                  ExecutionResources(cpu=1), EMPTY_DOWNSTREAM_USAGE
              ),
              ExecutionResources(cpu=1),
              [],
              True,
              "dummy",
              AutoscalingState(),
          )
          is o3
      )
      assert (
          select_operator_to_run(
              topo,
              TopologyResourceUsage(
                  ExecutionResources(cpu=1), EMPTY_DOWNSTREAM_USAGE
              ),
              ExecutionResources(cpu=1),
              [],
              False,
              "dummy",
              AutoscalingState(),
          )
          is None
      )
  
imports: import collections
  import time
  from unittest.mock import MagicMock
  import pytest
  import ray
  from ray._private.test_utils import run_string_as_driver_nonblocking, wait_for_condition
  from ray.data._internal.execution.interfaces import ExecutionOptions, ExecutionResources, PhysicalOperator
  from ray.data._internal.execution.interfaces.physical_operator import MetadataOpTask
  from ray.data._internal.execution.operators.input_data_buffer import InputDataBuffer
  from ray.data._internal.execution.operators.map_operator import MapOperator
  from ray.data._internal.execution.operators.map_transformer import create_map_transformer_from_block_fn
  from ray.data._internal.execution.streaming_executor import _debug_dump_topology, _validate_dag
  from ray.data._internal.execution.streaming_executor_state import AutoscalingState, DownstreamMemoryInfo, OpState, TopologyResourceUsage, _execution_allowed, build_streaming_topology, process_completed_tasks, select_operator_to_run, update_operator_states
  from ray.data._internal.execution.util import make_ref_bundles
  from ray.data.tests.conftest import *
  from ray.util.scheduling_strategies import NodeAffinitySchedulingStrategy
label_desc: Use image node_id 13 for calling a global function with example usage: test_select_ops_ensure_at_least_one_live_operator() without return types