svoid test_TreeSetWithDuplicates() {
  TreeSetWithDuplicates<S> set = new(comparatorFromCalculatedField(lambda0 l));
  set.addAll("hello", "world", "bla", "very long");
  assertEqualsOneOfVerbose(asList(set),
    ll("bla", "hello", "world", "very long"),
    ll("bla", "world", "hello", "very long"));
}