code: def test_custom_function(self):
      extension = extensions.ParameterStatistics(
          self.links, statistics=self.statistics
      )
      self.trainer.extend(extension)
      self.trainer.run()
  
      for value in six.itervalues(self.trainer.observation):
          self.assertEqual(value, self.expect)
  
imports: import re
  import time
  import unittest
  import mock
  import six
  import chainer
  from chainer import backend
  from chainer import testing
  from chainer import training
  from chainer.training import extensions
label_desc: Use image node_id 1 for calling the TestParameterStatisticsCustomFunction obj's underlying member method code with example usage: obj.test_custom_function() without return types