Renamed AbstractListenerRegistry to ListenerRegistry (since it is not abstract).
- added checkForNonRegistrant() predicate and augmented unit tests.

Change-Id: I7ecc618f01fdc4cead6f143a1e5e0ddd03268efc
diff --git a/core/net/src/main/java/org/onosproject/net/topology/impl/TopologyManager.java b/core/net/src/main/java/org/onosproject/net/topology/impl/TopologyManager.java
index 109f11f..956d7a6 100644
--- a/core/net/src/main/java/org/onosproject/net/topology/impl/TopologyManager.java
+++ b/core/net/src/main/java/org/onosproject/net/topology/impl/TopologyManager.java
@@ -21,7 +21,7 @@
 import org.apache.felix.scr.annotations.Reference;
 import org.apache.felix.scr.annotations.ReferenceCardinality;
 import org.apache.felix.scr.annotations.Service;
-import org.onosproject.event.AbstractListenerRegistry;
+import org.onosproject.event.ListenerRegistry;
 import org.onosproject.event.Event;
 import org.onosproject.event.EventDeliveryService;
 import org.onosproject.net.ConnectPoint;
@@ -69,8 +69,8 @@
 
     private final Logger log = getLogger(getClass());
 
-    private final AbstractListenerRegistry<TopologyEvent, TopologyListener>
-            listenerRegistry = new AbstractListenerRegistry<>();
+    private final ListenerRegistry<TopologyEvent, TopologyListener>
+            listenerRegistry = new ListenerRegistry<>();
 
     private TopologyStoreDelegate delegate = new InternalStoreDelegate();