flutter-graphql : how to mock watchQuery

Question

I am trying to add a stub to mock flutter-graphql watchQuery results to in a unit test but it seems complex because watchQuery returns an ObservableQuery which depends on QueryManager.

ObservableQuery watchQuery(WatchQueryOptions options) {
    options.policies =
        defaultPolicies.watchQuery.withOverrides(options.policies);
    return queryManager.watchQuery(options);
  }

Can someone provide an example for a watchQuery stub?