VOL-1888 Not enough info in ONU DGI to Identify the ONU.

         Fixed to fetch the serial number from the list of ONUs
         handled by the device handler from the onu-id and the
         intf-id which is sent by the openolt agent in the dgi
         indication.

Change-Id: I54342b9009d4d12c0efa3745d1f48567f183c245
diff --git a/adaptercore/openolt_eventmgr_test.go b/adaptercore/openolt_eventmgr_test.go
index 7de341f..dcfcef3 100644
--- a/adaptercore/openolt_eventmgr_test.go
+++ b/adaptercore/openolt_eventmgr_test.go
@@ -27,7 +27,13 @@
 
 func mockEventMgr() *OpenOltEventMgr {
 	ep := &mocks.MockEventProxy{}
-	return NewEventMgr(ep)
+	dh := &DeviceHandler{}
+	dh.onus = make(map[string]*OnuDevice)
+	dh.onus[dh.formOnuKey(1, 1)] = &OnuDevice{deviceID: "TEST_ONU",
+		deviceType:   "ONU",
+		serialNumber: "TEST_ONU_123",
+		onuID:        1, intfID: 1}
+	return NewEventMgr(ep, dh)
 }
 func TestOpenOltEventMgr_ProcessEvents(t *testing.T) {
 	em := mockEventMgr()