code: def test_backward_gpu(self):
      self.check_backward(
          cuda.to_gpu(self.s),
          cuda.to_gpu(self.i),
          cuda.to_gpu(self.gx),
          cuda.to_gpu(self.gt),
      )
  
imports: import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer import cuda
  from chainer import testing
  from chainer.testing import attr
  import thin_stack
label_desc: Use image node_id 7 for calling the TestThinStackGet obj's underlying member method code with example usage: obj.test_backward_gpu() without return types