Adding topology test suite.
diff --git a/core/trivial/src/main/java/org/onlab/onos/net/trivial/device/impl/SimpleDeviceManager.java b/core/trivial/src/main/java/org/onlab/onos/net/trivial/device/impl/SimpleDeviceManager.java
index 221a249..d037f2a 100644
--- a/core/trivial/src/main/java/org/onlab/onos/net/trivial/device/impl/SimpleDeviceManager.java
+++ b/core/trivial/src/main/java/org/onlab/onos/net/trivial/device/impl/SimpleDeviceManager.java
@@ -48,7 +48,7 @@
 
     private final Logger log = getLogger(getClass());
 
-    private final AbstractListenerRegistry<DeviceEvent, DeviceListener>
+    protected final AbstractListenerRegistry<DeviceEvent, DeviceListener>
             listenerRegistry = new AbstractListenerRegistry<>();
 
     private final SimpleDeviceStore store = new SimpleDeviceStore();