svoid test_compareCharIterators() {
  int tests = 0;
  for (S a : allABC(4))
    for (S b : allABC(4)) {
      ++tests;
      assertEquals(sign(cmp(a, b)), sign(compareCharIterators(charIterator(a), charIterator(b))));
    }
  print(nTests(tests) + " OK");
}