svoid test_joinSubstringObjects() {
  S s = "hello world";
  Substring x = joinSubstringObjects(ll(
    Substring(s, 0, 3), Substring(s, 3, 5), Substring(s, 5, 6)));
  assertEqualsVerbose("hello ", str(x));
  assertSameVerbose(s, x.baseString());
}