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());

  // test all cases of size update

  set.remove("x"); // remove element not in set

  assertEqualsVerbose(4, set.size());

  set.remove("bla"); // remove element without duplicates

  assertEqualsVerbose(3, set.size());

  set.remove("hello"); // remove element with a remaining duplicate

  assertEqualsVerbose(2, set.size());

  set.add("world"); // add existing element

  assertEqualsVerbose(2, set.size());

  set.add("old"); // add new element

  assertEqualsVerbose(3, set.size());

  set.add("new"); // add new element with existing duplicate

  assertEqualsVerbose(4, set.size());

  test_TreeSetWithDuplicates_2();

}

// test that elements with same probability are returned in

// insertion order

svoid test_TreeSetWithDuplicates_2() {

  TreeSetWithDuplicates<S> set = new(comparatorFromCalculatedField l());

  LS l = ll("abc", "xyz", "def", "ppp", "aaa");

  set.addAll(l);

  assertEqualsVerbose(l, asList(set));

}