code: def test_three_recurrent_children_cpu(self):
      self._test_mask_recurrent_state_at(gpu=-1)
  
imports: import unittest
  import chainer
  from chainer import functions
  from chainer import links
  from chainer import testing
  import numpy
  from chainerrl.links import StatelessRecurrentSequential
label_desc: Use image node_id 15 for calling the TestStatelessRecurrentSequential obj's underlying member method code with example usage: obj.test_three_recurrent_children_cpu() without return types