code: def test_double_backward_gpu(self):
      with chainer.using_config("use_cudnn", "always"):
          self.check_double_backward(
              cuda.to_gpu(self.x),
              cuda.to_gpu(self.t),
              cuda.to_gpu(self.gy),
              cuda.to_gpu(self.ggx),
              normalize=self.normalize,
              reduce="mean",
          )
  
imports: import math
  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
  from chainer import utils
label_desc: Use image node_id 20 for calling the TestSigmoidCrossEntropy obj's underlying member method code with example usage: obj.test_double_backward_gpu() without return types