code: def __call__(self, key, value):
      self.target[key] = value
      return self.target[key]
  
imports: import numpy
  import platform
  import pytest
  import unittest
  import chainer
  import chainer.testing
  import chainermn
label_desc: Use image node_id 3 for calling the DummySerializer obj's underlying member method code with example usage: obj.__call__(key, value) and returns: self