code: def availability_zone(self) -> Optional[str]:
      return self._availability_zone
  
imports: import asyncio
  import importlib
  import os
  import sys
  import time
  from typing import Optional, Set, Tuple, Union
  import pytest
  import ray
  from ray._private.utils import get_or_create_event_loop
  from ray.serve._private.common import DeploymentID
  from ray.serve._private.router import PowerOfTwoChoicesReplicaScheduler, Query, ReplicaWrapper, RequestMetadata
label_desc: Use image node_id 4 for calling the FakeReplicaWrapper obj's underlying member method code with example usage: obj.availability_zone() and returns: self