@Test
public void testSourceTopics() {

    final TopologyBuilder builder = new TopologyBuilder();
    builder.addSource("source-1", "topic-1");
    builder.addSource("source-2", "topic-2");
    builder.addSource("source-3", "topic-3");
    builder.addInternalTopic("topic-3");
    Set<String> expected = new HashSet<String>();
    expected.add("topic-1");
    expected.add("topic-2");
    expected.add("X-topic-3");
    assertEquals(expected, builder.sourceTopics("X"));
}