def test_change_list_add_no_duplicates(self):
        changed = self._add_list_test_helper('alice, bob', 'bob, carol')
        self.assertEqual(changed, 'alice, bob, carol')
Existing items are not duplicated.
dataset/ETHPy150Open edgewall/trac/trac/ticket/tests/batch.py/BatchModifyTestCase.test_change_list_add_no_duplicates