public Set<String> getSources() {
        return Collections.unmodifiableSet(sources);
    }
@Test
    public void testIterationOrder() {
        String[] hosts = new String[]{"primary", "fallback", "last-resort"};
        ConfigSourceSet css = new ConfigSourceSet(hosts);

        Set<String> sources = css.getSources();
        assertEquals(hosts.length, sources.size());
        int i = 0;
        for (String s : sources) {
            assertEquals(hosts[i++], s);
        }
    }