code: def test_backprop_step_gpu(self):
      self.setup_gpu()
      self.check_backprop_step((self.gx1_orig, self.gx2_orig))
  
imports: import unittest
  import mock
  import numpy
  import six
  import chainer
  from chainer import _backprop_utils
  from chainer.backends import cuda
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 9 for calling the TestFunctionNode obj's underlying member method code with example usage: obj.test_backprop_step_gpu() without return types