svoid test_TreeSetWithDuplicates() {
  TreeSetWithDuplicates<S> set = new(comparatorFromCalculatedField l());
  set.addAll(ll("hello", "world", "bla", "very long"));
  assertEqualsOneOfVerbose(asList(set),
    ll("bla", "hello", "world", "very long"),
    ll("bla", "world", "hello", "very long"));
  assertEqualsVerbose(4, set.size());
  set.remove("x");
  assertEqualsVerbose(4, set.size());
  set.remove("bla");
  assertEqualsVerbose(3, set.size());
  set.remove("hello");
  assertEqualsVerbose(2, set.size());
  set.add("world");
  assertEqualsVerbose(2, set.size());
}