code: def forward(self, inputs, device):
      c1, c2, x1, x2 = inputs
      out = functions.slstm(c1, c2, x1, x2)
      return out
  
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 TestSLSTM obj's underlying member method code with example usage: obj.forward(inputs, device) and returns: out