mixin TestMixin<R, T> {
  Future<T> test(Future<R> fetch) async {}
}

class PagingResponse<T> {
  final PagingResponseData<T> data;
  PagingResponse(this.data);
}

class PagingResponseData<T> {
  final List<T> data;
  PagingResponseData(this.data);
}

class Response<T> {
  final T data;
  Response(this.data);
}

class Class1 with TestMixin<Response<String>, String> {
  _test() {}
}

class Class2 with TestMixin<PagingResponse<String>, String> {
  _test() {}
}

main() {}