code: def test_backward(self, backend_config):
      self.check_backward(
          self.inputs, self.grad_outputs, backend_config
      )
  
imports: import unittest
  import numpy
  import six
  from chainer.backends import cuda
  from chainer import functions
  from chainer.functions.rnn import slstm
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import backend
label_desc: Use image node_id 3 for calling the TestSLSTMGrad obj's underlying member method code with example usage: obj.test_backward(backend_config) without return types