static <A extends Set<S>> void test_TreeSetDropIn(IF0<A> makeSet, IVF1<A> checkInternalStructure default null) {
  LS list = repF(1000, () -> randomID(3));
  Set<S> set = asTreeSet(list);
  A cset = makeSet!;
  addAll(cset, set);
  print(set);
  print(cset);
  assertEquals(asList(set), asList(cset));
  assertEqualsVerbose(l(set), l(cset));
  
  for (S a : shuffledIterator(list)) {
    set.remove(a);
    cset.remove(a);
    assertEquals(asList(set), asList(cset));
    assertEqualsVerbose(l(set), l(cset));
    pcallF(checkInternalStructure, cset);
  }
}

Began life as a copy of #1030939