[ONOS-3110] Port pair manager test case fixed

Change-Id: I7962527669e45dc7b4eb3e84dadcf9f059177bb5
diff --git a/apps/vtn/vtnrsc/src/test/java/org/onosproject/vtnrsc/portpair/impl/PortPairManagerTest.java b/apps/vtn/vtnrsc/src/test/java/org/onosproject/vtnrsc/portpair/impl/PortPairManagerTest.java
index c936d7c..6608512 100644
--- a/apps/vtn/vtnrsc/src/test/java/org/onosproject/vtnrsc/portpair/impl/PortPairManagerTest.java
+++ b/apps/vtn/vtnrsc/src/test/java/org/onosproject/vtnrsc/portpair/impl/PortPairManagerTest.java
@@ -26,6 +26,9 @@
 import org.onosproject.vtnrsc.TenantId;
 import org.onosproject.vtnrsc.DefaultPortPair;
 import org.onosproject.vtnrsc.util.VtnStorageServiceTest;
+import org.onosproject.common.event.impl.TestEventDispatcher;
+
+import static org.onosproject.net.NetTestTools.injectEventDispatcher;
 
 /**
  * Unit tests for PortPairManager class.
@@ -49,6 +52,7 @@
     public void testCreatePortPair() {
         // initialize port pair manager
         portPairMgr.storageService = storageService;
+        injectEventDispatcher(portPairMgr, new TestEventDispatcher());
         portPairMgr.activate();
 
         // create port pair