text: import unittest
  
  from . import oldest_unique
  
  
  class OldestUniqueTestCase(unittest.TestCase):
      def test_oldest_unique(self):
          o = oldest_unique.OldestUnique()
          self.assertIsNone(o.query())
          o.feed('a')
          self.assertEqual(o.query(), 'a')
          o.feed('a')
          self.assertIsNone(o.query())
          o.feed('a')
          self.assertIsNone(o.query())
          for c in 'bcdefbce':
              o.feed(c)
          self.assertEqual(o.query(), 'd')
  