code: def check_backward(self, x_data, y_grad):
      gradient_check.check_backward(
          self.link,
          x_data,
          y_grad,
          (self.link.W, self.link.b),
          eps=1e-2,
          atol=5e-5,
          rtol=5e-4,
      )
  
imports: import unittest
  import numpy
  import six.moves.cPickle
  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.utils import conv
label_desc: Use image node_id 7 for calling the TestDilatedConvolution2DParameterShapePlaceholder obj's underlying member method code with example usage: obj.check_backward(x_data, y_grad) without return types