strings.add("four");
    assertEquals(ImmutableMap.of("one", 3, "two", 3, "three", 5, "four", 4), map);
    assertEquals(Integer.valueOf(4), map.get("four"));
  }

  public void testAsMapWritesThrough() {
    Set<String> strings = Sets.newLinkedHashSet();
    Collections.addAll(strings, "one", "two", "three");
    Map<String, Integer> map = Maps.asMap(strings, LENGTH_FUNCTION);