Add a check to make sure that during state conflict res we only request a PDU we don't have.

tests/test_state.py

@@ -37,6 +37,7 @@ class StateTestCase(unittest.TestCase):
             "update_current_state",
             "get_latest_pdus_in_context",
             "get_current_state",
+            "get_pdu",
         ])
         self.replication = Mock(spec=["get_pdu"])
 
@@ -220,6 +221,8 @@ class StateTestCase(unittest.TestCase):
 
         self.replication.get_pdu.side_effect = set_return_tree
 
+        self.persistence.get_pdu.return_value = None
+
         is_new = yield self.state.handle_new_state(new_pdu)
 
         self.assertTrue(is_new)