public final boolean offer(int queueIndex, E item) {
        return offer(queues[queueIndex], item);
    }
@Test
    public void when_offerToGivenQueue_then_poll() {
        // when
        boolean didOffer = conveyor.offer(defaultQ, item1);

        // then
        assertTrue(didOffer);
        assertSame(item1, defaultQ.poll());
    }