code: def check_backward(self, x_data, y_grad):
      gradient_check.check_backward(
          self.link,
          x_data,
          y_grad,
          (
              self.link.plain.W,
              self.link.plain.b,
              self.link.transform.W,
              self.link.transform.b,
          ),
          eps=1e-2,
          atol=3.2e-3,
          rtol=1e-2,
      )
  
file_path: chainer/tests/chainer_tests/links_tests/connection_tests/test_highway.py
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 6 for calling the TestHighway obj's underlying member method code with example usage: obj.check_backward(x_data, y_grad) without return types