@Test
public void testNotAmong() {

  Parser<Void> scanner = Scanners.notAmong("ab");
  assertNull(scanner.parse("0"));
  assertScanner(mode, scanner, "0a", "a");
  assertFailure(mode, scanner, "a", 1, 1, "^[ab] expected, a encountered.");
  assertFailure(mode, scanner, "b", 1, 1);
  assertFailure(mode, scanner, "", 1, 1);
}