Fix UserVisibilityMediatorVisibleBackgroundUserTestCase

The listener was not verified in the test
testStartVisibleBgUser_onSecondaryDisplay_displayAvailable.

Fixes: 271182814

Test: atest UserVisibilityMediatorMUMDTest \
	    UserVisibilityMediatorMUPANDTest

Change-Id: Id2cf50aeaea5a70eb38a07292bae97d97a622d09

services/tests/mockingservicestests/src/com/android/server/pm/UserVisibilityMediatorVisibleBackgroundUserTestCase.java

@@ -160,6 +160,8 @@ abstract class UserVisibilityMediatorVisibleBackgroundUserTestCase
 
         assertUserCanBeAssignedExtraDisplay(USER_ID, OTHER_SECONDARY_DISPLAY_ID);
 
+        listener.verify();
+
         // Assign again, without unassigning (to make sure it becomes invisible on stop)
         AsyncUserVisibilityListener listener2 = addListenerForEvents(onInvisible(USER_ID));
         assertUserCanBeAssignedExtraDisplay(USER_ID, OTHER_SECONDARY_DISPLAY_ID,