code: def check_backward(self, xs, gy):
      # Numerical gradient dos not work with non-finite values.
      # Gradients for integer values are not defined.
      if (
          not numpy.isfinite(self.pad)
          or numpy.dtype(self.dtype).kind != "f"
      ):
          return
  
      def f(*xs):
          return functions.pad_sequence(
              xs, length=self.length, padding=self.pad
          )
  
      gradient_check.check_backward(f, xs, gy, dtype=numpy.float64)
  
imports: import contextlib
  import unittest
  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
label_desc: Use image node_id 5 for calling the TestPadSequence obj's underlying member method code with example usage: obj.check_backward(xs, gy) and returns: functions