code: def check_backward(
      self, t_data, xs_data, l_length, x_length, gy_data
  ):
      def f(input_length, label_length, t, *x):
          return functions.connectionist_temporal_classification(
              x,
              t,
              self.blank_symbol,
              x_length,
              l_length,
              reduce=self.reduce,
          )
  
      gradient_check.check_backward(
          f,
          (x_length, l_length, t_data) + xs_data,
          gy_data,
          eps=1e-2,
          **self.check_backward_options,
      )
  
imports: import math
  import unittest
  import numpy
  import chainer
  from chainer import backend
  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 condition
label_desc: Use image node_id 8 for calling the CTCTestBase obj's underlying member method code with example usage: obj.check_backward(t_data, xs_data, l_length, x_length, gy_data) and returns: functions