fix: test case

Author: xianml

uvicorn/server.py

@@ -310,8 +310,9 @@ async def _wait_tasks_to_complete(self) -> None:
             while self.server_state.tasks and not self.force_exit:
                 await asyncio.sleep(0.1)
 
-        for server in self.servers:
-            await server.wait_closed()
+        if hasattr(self, "servers") and self.servers:
+            for server in self.servers:
+                await server.wait_closed()
 
     @contextlib.contextmanager
     def capture_signals(self) -> Generator[None, None, None]: