code: def test_backward_gpu(self):
      with testing.assert_warns(DeprecationWarning):
          self.l.to_gpu()
      self.check_backward(cuda.to_gpu(self.x), cuda.to_gpu(self.gy))
  
imports: import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import function_hooks
  from chainer import functions
  from chainer.functions.math import basic_math
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 6 for calling the TestCupyMemoryProfileHookToLink obj's underlying member method code with example usage: obj.test_backward_gpu() without return types