code: def check_backward(self, h_data, xs_data, gh_data, gys_data):
      def fun(*args):
          if self.hidden_none:
              h = None
              xs = args
          else:
              (h,) = args[:1]
              xs = args[1:]
          hy, ys = self.rnn(h, xs)
          return tuple(
              [
                  hy,
              ]
              + list(ys)
          )
  
      params = []
      for layer in self.rnn:
          for p in layer.params():
              params.append(p)
  
      if self.hidden_none:
          in_data = xs_data
      else:
          in_data = [h_data] + xs_data
      gradient_check.check_backward(
          fun,
          tuple(in_data),
          tuple([gh_data] + gys_data),
          tuple(params),
          eps=1e-2,
          rtol=1e-3,
          atol=1e-3,
      )
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import gradient_check
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 10 for calling the TestNStepBiGRU obj's underlying member method code with example usage: obj.check_backward(h_data, xs_data, gh_data, gys_data) and returns: tuple