code: def check_backward(self, x_data, y_grad):
      gradient_check.check_backward(
          self.link, x_data, y_grad, self.link.W, atol=1e-4, rtol=1e-3
      )
  
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
label_desc: Use image node_id 7 for calling the TestEmbedID obj's underlying member method code with example usage: obj.check_backward(x_data, y_grad) without return types