public void testImmutableMapCopyOfImmutableSortedMap() {
    IntegerDiv10 three = new IntegerDiv10(3);
    IntegerDiv10 eleven = new IntegerDiv10(11);
    IntegerDiv10 twelve = new IntegerDiv10(12);
    IntegerDiv10 twenty = new IntegerDiv10(20);
    Map<IntegerDiv10, String> original =
        ImmutableSortedMap.of(three, "three", eleven, "eleven", twenty, "twenty");
    Map<IntegerDiv10, String> copy = ImmutableMap.copyOf(original);