def test_equal_1(self):
     self.assertEqual(list(sort([])), [])
 def test_equal_2(self):
     self.assertEqual(list(sort(['z', 'x', 'w', 'y'])),
                      ['w', 'x', 'y', 'z'])
 def test_equal_3(self):
     self.assertEqual(list(sort(['b', 'ba', 'ab', 'bb', 'c'])),
                      ['ab', 'b', 'ba', 'bb', 'c'])