code: def test_gpu(self):
      x = cuda.to_gpu(self.x)
      with chainer.using_config("use_cudnn", "never"):
          self._check(x)
      with chainer.using_config("use_cudnn", "always"):
          self._check(x)
  
imports: import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import backend
  from chainer_tests.functions_tests.pooling_tests import pooling_nd_helper
label_desc: Use image node_id 4 for calling the TestMaxPooling2DIndices obj's underlying member method code with example usage: obj.test_gpu() without return types