code: def check_double_backward(self, x_data, t_data, gy_data, ggx_data):
      def f(x):
          return functions.select_item(x, t_data)
  
      gradient_check.check_double_backward(
          f,
          x_data,
          gy_data,
          ggx_data,
          eps=0.01,
          dtype="d",
          **self.check_backward_options,
      )
  
imports: import unittest
  import numpy
  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
label_desc: Use image node_id 8 for calling the TestSelectItem obj's underlying member method code with example usage: obj.check_double_backward(x_data, t_data, gy_data, ggx_data) and returns: functions