@Override
    public Iterator<Uuid> iterator() {
        return new TopicIdIterator(topicNames.iterator(), image);
    }
@Test
    public void testIterator() {
        Uuid fooUuid = Uuid.randomUuid();
        Uuid barUuid = Uuid.randomUuid();
        Uuid bazUuid = Uuid.randomUuid();
        Uuid quxUuid = Uuid.randomUuid();
        TopicsImage topicsImage = new MetadataImageBuilder()
            .addTopic(fooUuid, "foo", 3)
            .addTopic(barUuid, "bar", 3)
            .addTopic(bazUuid, "baz", 3)
            .addTopic(quxUuid, "qux", 3)
            .build()
            .topics();

        Set<Uuid> topicIds = new TopicIds(mkSet("foo", "bar", "baz", "qux"), topicsImage);
        Set<Uuid> expectedIds = mkSet(fooUuid, barUuid, bazUuid, quxUuid);
        Set<Uuid> actualIds = new HashSet<>(topicIds);

        assertEquals(expectedIds, actualIds);
    }