fix testsuite: apply hardening to awaiting grpc server stop

8bca31f1261ef8a4780968732402052c1ff28f34

Author: Anton3

testsuite/pytest_plugins/pytest_userver/plugins/grpc/mockserver.py

@@ -84,14 +84,25 @@ async def grpc_mockserver(grpc_mockserver_endpoint) -> grpc.aio.Server:
     """
     server = grpc.aio.server()
     server.add_insecure_port(grpc_mockserver_endpoint)
-    server_task = asyncio.create_task(server.start())
+    await server.start()
 
     try:
         yield server
     finally:
-        await asyncio.shield(server.stop(grace=None))
-        await asyncio.shield(server.wait_for_termination())
-        await asyncio.shield(server_task)
+
+        async def stop_server():
+            await server.stop(grace=None)
+            await server.wait_for_termination()
+
+        stop_server_task = asyncio.shield(asyncio.create_task(stop_server()))
+        # asyncio.shield does not protect our await from cancellations, and we
+        # really need to wait for the server stopping before continuing.
+        try:
+            await stop_server_task
+        except asyncio.CancelledError:
+            await stop_server_task
+            # Propagate cancellation when we are done
+            raise
 
 
 @pytest.fixture(scope='session')