code: def test_gpu(self):
      self._test(chainer.cuda.cupy)
  
imports: import unittest
  import chainer
  import chainer.links
  from chainer import testing
  import numpy
  import basetest_dqn_like
  from basetest_training import _TestBatchTrainingMixin
  import chainerrl
  from chainerrl.agents import categorical_dqn
  from chainerrl.agents.categorical_dqn import compute_value_loss
  from chainerrl.agents.categorical_dqn import compute_weighted_value_loss
  from chainerrl.agents import CategoricalDQN
label_desc: Use image node_id 4 for calling the TestApplyCategoricalProjectionToManualCases obj's underlying member method code with example usage: obj.test_gpu() without return types