Update the TopologyEvents internals to use ImmutableList to store a copy
of the events.

Add unit test that class TopologyEvents is immutable.

Change-Id: Iade68fe43907fbd0eedd0fff86eb5fbb560da9f5
diff --git a/src/test/java/net/onrc/onos/core/topology/TopologyManagerTest.java b/src/test/java/net/onrc/onos/core/topology/TopologyManagerTest.java
index a84b00f..ae783cc 100644
--- a/src/test/java/net/onrc/onos/core/topology/TopologyManagerTest.java
+++ b/src/test/java/net/onrc/onos/core/topology/TopologyManagerTest.java
@@ -9,6 +9,7 @@
 import net.onrc.onos.core.registry.RegistryException;
 import net.onrc.onos.core.util.Dpid;
 import net.onrc.onos.core.util.EventEntry;
+import static net.onrc.onos.core.util.ImmutableClassChecker.assertThatClassIsImmutable;
 import net.onrc.onos.core.util.OnosInstanceId;
 import net.onrc.onos.core.util.PortNumber;
 import net.onrc.onos.core.util.SwitchPort;
@@ -202,6 +203,14 @@
     }
 
     /**
+     * Tests the immutability of {@link TopologyEvents}.
+     */
+    @Test
+    public void testImmutableTopologyEvents() {
+        assertThatClassIsImmutable(TopologyEvents.class);
+    }
+
+    /**
      * Test the Switch Mastership Updated Event.
      */
     @Test