new ImmutableBiMap.Builder<Integer, String>()
          .put(1, "one")
          .put(2, "two")
          .put(3, "three")
          .build();

  public void testUniqueIndexCollection() {
    ImmutableMap<Integer, String> outputMap =
        Maps.uniqueIndex(INT_TO_STRING_MAP.values(), Functions.forMap(INT_TO_STRING_MAP.inverse()));
    assertEquals(INT_TO_STRING_MAP, outputMap);
  }