Adding more unit tests.
Made some classes abstract which should have been.
diff --git a/core/api/src/main/java/org/onlab/onos/net/AbstractAnnotated.java b/core/api/src/main/java/org/onlab/onos/net/AbstractAnnotated.java
index f29ad43..c329598 100644
--- a/core/api/src/main/java/org/onlab/onos/net/AbstractAnnotated.java
+++ b/core/api/src/main/java/org/onlab/onos/net/AbstractAnnotated.java
@@ -5,7 +5,7 @@
 /**
  * Base abstraction of an annotated entity.
  */
-public class AbstractAnnotated implements Annotated {
+public abstract class AbstractAnnotated implements Annotated {
 
     private static final Annotations EMPTY = DefaultAnnotations.builder().build();