Maps.uniqueIndex(
            INT_TO_STRING_MAP.values().iterator(), Functions.forMap(INT_TO_STRING_MAP.inverse()));
    assertEquals(INT_TO_STRING_MAP, outputMap);
  }

  /** Can't create the map if more than one value maps to the same key. */
  public void testUniqueIndexDuplicates() {
    try {
      Map<Integer, String> unused =
          Maps.uniqueIndex(ImmutableSet.of("one", "uno"), Functions.constant(1));