static <A, C extends Collection<A>> C assertContainsVerbose(S msg default null, C c, A y) {
  printVars("assertContainsVerbose", +msg, +c, +y);
  if (!contains(c, y))
    fail((msg != null ? msg + ": " : "") + y + " not contained in " + c);
  ret c;
}

sS assertContainsVerbose(S b, S a) {
  printVars("assertContainsVerbose", +a, +b);
  if (!contains(a, b))
    fail(quote(b) + " not contained in " + quote(a));
  ret a;
}

Began life as a copy of #1012660