code: def check_backward(self, x, gy):
      x = chainer.Variable(x)
      y = self.l(x)
      y.grad = gy
      with self.h:
          y.backward()
      # It includes forward of + that accumulates gradients to W and b
      self.assertEqual(3, len(self.h.call_history))
      for entry in self.h.call_history:
          if entry[0] == "Add":
              continue
          check_history(self, entry, basic_math.Mul, int, int)
  
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 5 for calling the TestCupyMemoryProfileHookToLink obj's underlying member method code with example usage: obj.check_backward(x, gy) without return types