code: def output(self):
      return self.make_target("./test/dummy.pkl")
  
imports: import logging
  import os
  import unittest
  from copy import copy
  import luigi
  import luigi.mock
  import gokart
  from gokart.build import GokartBuildError, LoggerConfig
label_desc: Use image node_id 1 for calling the _DummyTask obj's underlying member method code with example usage: obj.output() and returns: self