Enhancing driver subsystem to support asynchronous event notifications.

Change-Id: I6850aae4f660b8328378da98460529eb58531732
diff --git a/core/api/src/test/java/org/onosproject/net/driver/DriverServiceAdapter.java b/core/api/src/test/java/org/onosproject/net/driver/DriverServiceAdapter.java
index 813befc..b2644db 100644
--- a/core/api/src/test/java/org/onosproject/net/driver/DriverServiceAdapter.java
+++ b/core/api/src/test/java/org/onosproject/net/driver/DriverServiceAdapter.java
@@ -53,4 +53,12 @@
     public Driver getDriver(String driverName) {
         return null;
     }
+
+    @Override
+    public void addListener(DriverListener listener) {
+    }
+
+    @Override
+    public void removeListener(DriverListener listener) {
+    }
 }