code: def test_double_backward_gpu(self):
      self.check_double_backward(
          [cuda.to_gpu(x) for x in self.xs],
          cuda.to_gpu(self.gy),
          [cuda.to_gpu(ggx) for ggx in self.ggxs],
      )
  
imports: import contextlib
  import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 10 for calling the TestPadSequence obj's underlying member method code with example usage: obj.test_double_backward_gpu() without return types