new_contents: import unittest
  
  import numpy as np
  
  from chainercv.evaluations import eval_semantic_segmentation
  
  
  class TestEvalSemanticSegmentation(unittest.TestCase):
  
      def test_eval_semantic_segmentation(self):
          predict = np.array([[1, 1, 0], [0, 0, 1]]).reshape(1, 2, 3)
          gt = np.array([[1, 0, 0], [0, -1, 1]]).reshape(1, 2, 3)
          # p_00 = 2
          # p_01 = 1
          # p_10 = 0
          # p_11 = 2
          acc, acc_cls, mean_iu, fwavacc = eval_semantic_segmentation(
              predict, gt, n_class=2)
  
          self.assertEqual(acc, 4. / 5.)
          self.assertEqual(acc_cls, 1. / 2. * (1 + 2. / 3.))
          self.assertEqual(mean_iu, 1. / 2. * (1. / 3. + 1))
          self.assertEqual(fwavacc, 1. / 5. * (2. + 4. / 3.))
  
subject: add test