### Question:
MemcachedSet implements Iterable<String> { static String encodeSet(Set<String> pageIds) { if (pageIds.isEmpty()) { return ""; } else { return PLUS + Strings.join(" +", pageIds.toArray(new String[pageIds.size()])); } } MemcachedSet(MemcachedClient client, String key, int expirationTime); @Override Iterator<String> iterator(); boolean add(String value); boolean remove(String value); void compact(); void compact(Predicate<String> predicate);  }### Answer:
@Test public void encode() { assertEquals("", MemcachedSet.encodeSet(new HashSet<>())); assertEquals("+1 +2 +3", MemcachedSet.encodeSet(new HashSet<>(Arrays.asList("1", "2", "3")))); }