code: def test_backward_gpu(self):
      with testing.assert_warns(DeprecationWarning):
          self.link.to_gpu()
      self.link(cuda.cupy.zeros(self.shape, dtype="f"))
      self.check_backward(cuda.to_gpu(self.x), cuda.to_gpu(self.gy))
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import gradient_check
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
  from chainer.utils import type_check
label_desc: Use image node_id 9 for calling the LayerNormalizationTest obj's underlying member method code with example usage: obj.test_backward_gpu() without return types