Added unit tests for the event abstractions.
Added Element as the notion of common ancestry between Device and Host.
diff --git a/net/api/src/main/java/org/onlab/onos/event/AbstractListenerManager.java b/net/api/src/main/java/org/onlab/onos/event/AbstractListenerManager.java
index 7d4836f..d063b59 100644
--- a/net/api/src/main/java/org/onlab/onos/event/AbstractListenerManager.java
+++ b/net/api/src/main/java/org/onlab/onos/event/AbstractListenerManager.java
@@ -51,8 +51,13 @@
         }
     }
 
-    @Override
-    public void reportProblem(E event, Throwable error) {
+    /**
+     * Reports a problem encountered while processing an event.
+     *
+     * @param event event being processed
+     * @param error error encountered while processing
+     */
+    protected void reportProblem(E event, Throwable error) {
         log.warn("Exception encountered while processing event " + event, error);
     }
 
diff --git a/net/api/src/main/java/org/onlab/onos/event/AbstractEventSinkBroker.java b/net/api/src/main/java/org/onlab/onos/event/DefaultEventSinkBroker.java
similarity index 91%
rename from net/api/src/main/java/org/onlab/onos/event/AbstractEventSinkBroker.java
rename to net/api/src/main/java/org/onlab/onos/event/DefaultEventSinkBroker.java
index 4ca3c3c..c791544 100644
--- a/net/api/src/main/java/org/onlab/onos/event/AbstractEventSinkBroker.java
+++ b/net/api/src/main/java/org/onlab/onos/event/DefaultEventSinkBroker.java
@@ -12,7 +12,7 @@
 /**
  * Base implementation of event sink broker.
  */
-public class AbstractEventSinkBroker implements EventSinkBroker {
+public class DefaultEventSinkBroker implements EventSinkBroker {
 
     private final Map<Class<? extends Event>, EventSink<? extends Event>> sinks =
             new ConcurrentHashMap<>();
@@ -36,6 +36,7 @@
     @Override
     @SuppressWarnings("unchecked")
     public <E extends Event> EventSink<E> getSink(Class<E> eventClass) {
+        // TODO: add implicit registration of descendant classes
         return (EventSink<E>) sinks.get(eventClass);
     }
 
diff --git a/net/api/src/main/java/org/onlab/onos/event/EventSink.java b/net/api/src/main/java/org/onlab/onos/event/EventSink.java
index f46458c..45ad408 100644
--- a/net/api/src/main/java/org/onlab/onos/event/EventSink.java
+++ b/net/api/src/main/java/org/onlab/onos/event/EventSink.java
@@ -12,12 +12,4 @@
      */
     void process(E event);
 
-    /**
-     * Reports a problem encountered while processing an event.
-     *
-     * @param event event being processed
-     * @param error error encountered while processing
-     */
-    void reportProblem(E event, Throwable error);
-
 }