public void addNotificationFilter(NotificationFilter another) {
        checkForDuplicates(another);
        notificationFilters.add(another);
    }
@Test
    void shouldThrowExceptionIfFilterWithSameEventAlreadyExist() {
        User user = new User("foo");
        user.addNotificationFilter(new NotificationFilter("cruise", "dev", StageEvent.Fixed, false));
        try {
            user.addNotificationFilter(new NotificationFilter("cruise", "dev", StageEvent.Fixed, false));
            fail("shouldThrowExceptionIfFilterWithSameEventAlreadyExist");
        } catch (Exception e) {
            assertThat(e.getMessage()).contains("Duplicate notification filter");
        }
    }