code: def test_counting_iterator_index(self, ref=None, itr=None):
      # Test the indexing functionality of CountingIterator
      if ref is None:
          assert itr is None
          ref = list(range(10))
          itr = iterators.CountingIterator(ref)
      else:
          assert len(ref) == 10
          assert itr is not None
  
      self.assertTrue(itr.has_next())
      self.assertEqual(itr.n, 0)
      self.assertEqual(next(itr), ref[0])
      self.assertEqual(itr.n, 1)
      self.assertEqual(next(itr), ref[1])
      self.assertEqual(itr.n, 2)
      itr.skip(3)
      self.assertEqual(itr.n, 5)
      self.assertEqual(next(itr), ref[5])
      itr.skip(2)
      self.assertEqual(itr.n, 8)
      self.assertEqual(list(itr), [ref[8], ref[9]])
      self.assertFalse(itr.has_next())
  
file_path: fairseq/tests/test_iterators.py
imports: import unittest
  from fairseq.data import iterators, ListDataset
label_desc: Use image node_id 1 for calling the TestIterators obj's underlying member method code with example usage: obj.test_counting_iterator_index(ref, itr) without return types