test_fails

======================================================================
FAIL: test_replicate_object_with_exception (test.unit.common.test_db_replicator.TestDBReplicator)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/stack/swift/test/unit/common/test_db_replicator.py", line 679, in test_replicate_object_with_exception
    do_test(replicator.ring.devs[3]['id'], 1, [1, 2, 3, 5])
  File "/opt/stack/swift/test/unit/common/test_db_replicator.py", line 674, in do_test
    self.assertEqual(expected_to_repl, called_devices)
AssertionError: Lists differ: [1, 2, 3, 5] != [1, 2, 3, 4]

First differing element 3:
5
4

- [1, 2, 3, 5]
?           ^

+ [1, 2, 3, 4]
?           ^

    """Fail immediately, with the given message."""
>>  raise self.failureException('Lists differ: [1, 2, 3, 5] != [1, 2, 3, 4]\n\nFirst differing element 3:\n5\n4\n\n- [1, 2, 3, 5]\n?           ^\n\n+ [1, 2, 3, 4]\n?           ^\n')


----------------------------------------------------------------------
Ran 64 tests in 0.553s

FAILED (failures=1)

tracing_repl_to_node.diff

diff --git a/test/unit/common/test_db_replicator.py b/test/unit/common/test_db_replicator.py
index a1a18fe..9949279 100644
--- a/test/unit/common/test_db_replicator.py
+++ b/test/unit/common/test_db_replicator.py
@@ -648,27 +648,41 @@ class TestDBReplicator(unittest.TestCase):
         replicator.ring = FakeRingWithNodes().Ring('path')
         replicator.brokerclass = FakeAccountBroker
         replicator.delete_db = self.stub_delete_db
+
         replicator._repl_to_node = mock.Mock(side_effect=Exception())
         replicator._replicate_object('0', '/path/to/file',
                                      replicator.ring.devs[0]['id'])
         self.assertEqual(2, replicator._repl_to_node.call_count)
+
+        def do_test(local_node, fail_count, expected_to_repl):
+            called_devices = []
+            fail_counter = [fail_count]
+
+            def fake_repl_to_node(
+                    node, broker, partition, info, different_region):
+                called_devices.append(node['id'])
+                if fail_counter[0]:
+                    fail_counter[0] -= 1
+                    raise DriveNotMounted()
+                else:
+                    return True
+
+            with mock.patch.object(
+                    replicator, '_repl_to_node', fake_repl_to_node):
+                replicator._replicate_object('0', '/path/to/file', local_node)
+
+            self.assertEqual(expected_to_repl, called_devices)
+
         # with one DriveNotMounted exception called on +1 more replica
-        replicator._repl_to_node = mock.Mock(side_effect=[DriveNotMounted()])
-        replicator._replicate_object('0', '/path/to/file',
-                                     replicator.ring.devs[0]['id'])
-        self.assertEqual(3, replicator._repl_to_node.call_count)
+        do_test(replicator.ring.devs[0]['id'], 1, [2, 3, 4])
         # called on +1 more replica when *first* handoff and self
-        replicator._repl_to_node = mock.Mock(side_effect=[DriveNotMounted()])
-        replicator._replicate_object('0', '/path/to/file',
-                                     replicator.ring.devs[3]['id'])
-        self.assertEqual(4, replicator._repl_to_node.call_count)
+        do_test(replicator.ring.devs[3]['id'], 1, [1, 2, 3, 5])
+        # even if it's the last handoff it works to keep 3 replicas
+        # 2 primaries + 1 handoff
+        do_test(replicator.ring.devs[-1]['id'], 1, [1, 2, 3, 4])
         # with two DriveNotMounted exceptions called on +2 more replica keeping
         # durability
-        replicator._repl_to_node = mock.Mock(
-            side_effect=[DriveNotMounted()] * 2)
-        replicator._replicate_object('0', '/path/to/file',
-                                     replicator.ring.devs[0]['id'])
-        self.assertEqual(4, replicator._repl_to_node.call_count)
+        do_test(replicator.ring.devs[0]['id'], 2, [2, 3, 4, 5])
 
     def test_replicate_object_with_exception_run_out_of_nodes(self):
         replicator = TestReplicator({})