How to use the gdbgui.backend.app function in gdbgui

def test_connect(self):
        app = backend.app
        socketio = SocketIO()

        @socketio.on("connect")
        def on_connect():
            send({"connected": "foo"}, json=True)

        socketio.init_app(app, cookie="foo")
        client = socketio.test_client(app)
        received = client.get_received()
        self.assertEqual(len(received), 1)
        self.assertEqual(received[0]["args"], {"connected": "foo"})