code: def test_double_backward(self, backend_config):
      self.check_double_backward(
          self.inputs,
          self.grad_outputs,
          self.grad_grad_inputs,
          backend_config,
      )
  
imports: import unittest
  import warnings
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import backend
label_desc: Use image node_id 8 for calling the TestBatchNormalization obj's underlying member method code with example usage: obj.test_double_backward(backend_config) without return types