public long getBytesOutCounter() {
        return bytesOutFromRemovedSubscriptions.longValue()
                + sumSubscriptions(AbstractSubscription::getBytesOutCounter);
    }
@Test
    public void testGetBytesOutCounter() {
        topic.bytesOutFromRemovedSubscriptions.add(1L);
        when(subscription.getBytesOutCounter()).thenReturn(2L);
        assertEquals(topic.getBytesOutCounter(), 3L);
    }