fix: resolve test hang with websockets 14+

The test suite hangs after upgrading websockets from 13.x to 14.x/15.x
because websockets 14.0 switched to a new asyncio implementation by default.

Changes:
1. In TestServer.serve(): Replace deprecated asyncio.get_event_loop()
   pattern with asyncio.create_task() which is the modern way to create
   tasks when already inside an async context.

2. In serve_in_thread(): Instead of relying on server.run() which uses
   asyncio.run(), explicitly create a new event loop in the background
   thread with asyncio.new_event_loop() and asyncio.set_event_loop().

3. Remove loop="asyncio" from Config() since we now manage the event
   loop manually.

This approach is compatible with uvicorn 0.36+ (which removed the
deprecated setup_event_loop() method) and works with websockets 14+.

Fixes #3708

Author: SamMorrowDrums

tests/conftest.py

@@ -235,10 +235,9 @@ def install_signal_handlers(self) -> None:
     async def serve(self, sockets=None):
         self.restart_requested = asyncio.Event()
 
-        loop = asyncio.get_event_loop()
         tasks = {
-            loop.create_task(super().serve(sockets=sockets)),
-            loop.create_task(self.watch_restarts()),
+            asyncio.create_task(super().serve(sockets=sockets)),
+            asyncio.create_task(self.watch_restarts()),
         }
         await asyncio.wait(tasks)
 
@@ -269,7 +268,15 @@ async def watch_restarts(self) -> None:  # pragma: no cover
 
 
 def serve_in_thread(server: TestServer) -> typing.Iterator[TestServer]:
-    thread = threading.Thread(target=server.run)
+    def run_server():
+        loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(loop)
+        try:
+            loop.run_until_complete(server.serve())
+        finally:
+            loop.close()
+
+    thread = threading.Thread(target=run_server)
     thread.start()
     try:
         while not server.started:
@@ -282,6 +289,6 @@ def serve_in_thread(server: TestServer) -> typing.Iterator[TestServer]:
 
 @pytest.fixture(scope="session")
 def server() -> typing.Iterator[TestServer]:
-    config = Config(app=app, lifespan="off", loop="asyncio")
+    config = Config(app=app, lifespan="off")
     server = TestServer(config=config)
     yield from serve_in_thread(server)