[2856] Check that old_readers is untouched by add_reader()

src/lib/python/isc/memmgr/tests/datasrc_info_tests.py

@@ -99,6 +99,7 @@ class TestSegmentInfo(unittest.TestCase):
 
     def test_add_reader(self):
         self.assertSetEqual(self.__sgmt_info.get_readers(), set())
+        self.assertSetEqual(self.__sgmt_info.get_old_readers(), set())
         self.__sgmt_info.add_reader(1)
         self.assertSetEqual(self.__sgmt_info.get_readers(), {1})
         self.__sgmt_info.add_reader(3)
@@ -113,6 +114,9 @@ class TestSegmentInfo(unittest.TestCase):
         # but the existing readers must be untouched
         self.assertSetEqual(self.__sgmt_info.get_readers(), {1, 3, 2})
 
+        # none of this touches the old readers
+        self.assertSetEqual(self.__sgmt_info.get_old_readers(), set())
+
     def test_complete_update(self):
         # in READY state
         self.__si_to_ready_state()