code: def check_backward(self, x_data, y_grad):
      x = chainer.Variable(x_data)
      y = self.l(x)
      y.grad = y_grad
      y.backward()
  
file_path: chainercv/tests/links_tests/model_tests/mobilenet_tests/test_expanded_conv_2d.py
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import testing
  from chainermn import create_communicator
  from chainercv.links.model.mobilenet import ExpandedConv2D
  from chainercv.utils.testing import attr
label_desc: Use image node_id 5 for calling the TestExpandedConv2D obj's underlying member method code with example usage: obj.check_backward(x_data, y_grad) without return types