How to specify integration response for AWS websocket ApiGateway route

I don’t see how (or if it is possible) to specify an integration response for an AWS websocket ApiGateway route. Am I missing something? In general I think specifying route characteristics needs more to it.

I am also looking for how to specify this. In the obsoleted serverless-websockets-plugin, it could be specified in this way,

handler: handler.twoWay
  - websocket:
      routeKey: twoway
      # The property below will enable an integration response in the API Gateway.
      # See
      routeResponseSelectionExpression: $default

But it can’t be done now with my current version (1.43.0)

I have tried this, in wild hopes it would work, but it didn’t.

    handler: app/tests.handler
      - websocket:
          route: testWebsocket
          routeResponseSelectionExpression: $default

Found the issue on Github

Looking forward to the enhancement!