code: def test_mask_to_segm_index(self):
      index = np.arange(len(self.bbox))[::-1]
      segm = mask_to_segm(
          self.mask, self.bbox[::-1], self.segm_size, index=index
      )
      segm = segm[::-1]
      np.testing.assert_equal(segm, self.segm)
  
file_path: chainercv/tests/links_tests/model_tests/fpn_tests/test_mask_utils.py
imports: from __future__ import division
  import numpy
  import unittest
  from chainer import testing
  from chainercv.links.model.fpn.mask_utils import mask_to_segm
  from chainercv.links.model.fpn.mask_utils import segm_to_mask
label_desc: Use image node_id 4 for calling the TestMaskUtils obj's underlying member method code with example usage: obj.test_mask_to_segm_index() without return types