code: def test_redeploy_single_replica(serve_instance, use_handle):
      # Tests that redeploying a deployment with a single replica waits for the
      # replica to completely shut down before starting a new one.
      client = serve_instance
  
      name = "test"
  
      @ray.remote
      def call(block=False):
          if use_handle:
              handle = serve.get_deployment_handle(name, "app")
              ret = handle.handler.remote(block).result()
          else:
              ret = requests.get(
                  f"http://localhost:8000/{name}",
                  params={"block": block},
              ).text
  
          return ret.split("|")[0], ret.split("|")[1]
  
      signal_name = f"signal-{get_random_string()}"
      signal = SignalActor.options(name=signal_name).remote()
  
      @serve.deployment(name=name, version="1")
      class V1:
          async def handler(self, block: bool):
              if block:
                  signal = ray.get_actor(signal_name)
                  await signal.wait.remote()
  
              return f"1|{os.getpid()}"
  
          async def __call__(self, request):
              return await self.handler(
                  request.query_params["block"] == "True"
              )
  
      class V2:
          async def handler(self, *args):
              return f"2|{os.getpid()}"
  
          async def __call__(self, request):
              return await self.handler()
  
      serve.run(V1.bind(), name="app")
      ref1 = call.remote(block=False)
      val1, pid1 = ray.get(ref1)
      assert val1 == "1"
  
      # ref2 will block until the signal is sent.
      ref2 = call.remote(block=True)
      assert len(ray.wait([ref2], timeout=2.1)[0]) == 0
  
      # Redeploy new version. This should not go through until the old version
      # replica completely stops.
      V2 = V1.options(func_or_class=V2, version="2")
      serve.run(V2.bind(), _blocking=False, name="app")
      with pytest.raises(TimeoutError):
          client._wait_for_application_running("app", timeout_s=0.1)
  
      # It may take some time for the handle change to propagate and requests
      # to get sent to the new version. Repeatedly send requests until they
      # start blocking
      start = time.time()
      new_version_ref = None
      while time.time() - start < 30:
          ready, not_ready = ray.wait(
              [call.remote(block=False)], timeout=5
          )
          if len(ready) == 1:
              # If the request doesn't block, it must have been the old version.
              val, pid = ray.get(ready[0])
              assert val == "1"
              assert pid == pid1
          elif len(not_ready) == 1:
              # If the request blocks, it must have been the new version.
              new_version_ref = not_ready[0]
              break
      else:
          assert (
              False
          ), "Timed out waiting for new version to be called."
  
      # Signal the original call to exit.
      ray.get(signal.send.remote())
      val2, pid2 = ray.get(ref2)
      assert val2 == "1"
      assert pid2 == pid1
  
      # Now the goal and request to the new version should complete.
      client._wait_for_application_running("app")
      new_version_val, new_version_pid = ray.get(new_version_ref)
      assert new_version_val == "2"
      assert new_version_pid != pid2
  
imports: import os
  import sys
  import time
  from collections import defaultdict
  from typing import Callable
  import pytest
  import requests
  import ray
  from ray import serve
  from ray._private.pydantic_compat import ValidationError
  from ray._private.test_utils import SignalActor
  from ray.serve._private.utils import get_random_string
  from ray.serve.exceptions import RayServeException
label_desc: Use image node_id 4 for calling a global function with example usage: test_redeploy_single_replica(serve_instance, use_handle) and returns: ret,  ret, str, os, unknown, str, os, unknown