[Persistence] Add spec for failure dialog

WTD-1033.

platform/persistence/queue/test/PersistenceFailureConstantsSpec.js

@@ -7,7 +7,10 @@ define(
         "use strict";
 
         describe("Persistence failure constants", function () {
-
+            it("defines an overwrite key", function () {
+                expect(PersistenceFailureConstants.OVERWRITE_KEY)
+                    .toEqual(jasmine.any(String));
+            });
         });
     }
 );