code: def test_call(self):
      mean = self.evaluator()
      # main is used as default
      np.testing.assert_equal(mean["main/map"], self.expected_ap)
      np.testing.assert_equal(mean["main/ap/cls0"], np.nan)
      np.testing.assert_equal(mean["main/ap/cls1"], self.expected_ap)
      np.testing.assert_equal(mean["main/ap/cls2"], np.nan)
  
imports: import numpy
  import unittest
  import chainer
  from chainer.datasets import TupleDataset
  from chainer.iterators import SerialIterator
  from chainer import testing
  from chainercv.extensions import InstanceSegmentationVOCEvaluator
  from chainercv.utils.testing import attr
  from chainermn import create_communicator
label_desc: Use image node_id 3 for calling the TestInstanceSegmentationVOCEvaluator obj's underlying member method code with example usage: obj.test_call() without return types