code: def test_backward_cpu(self):
      self.check_backward(self.s, self.i, self.gx, 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 6 for calling the TestThinStackGet obj's underlying member method code with example usage: obj.test_backward_cpu() without return types