code: def check_backward(self, x_data):
      xp = backend.get_array_module(x_data)
      x = chainer.Variable(x_data)
      y = self.l(x)
      y.grad = xp.random.randn(*y.data.shape).astype("f")
      y.backward()
  
imports: import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 2 for calling the TestInceptionBNBase obj's underlying member method code with example usage: obj.check_backward(x_data) without return types