@Test
public void testAmong_oneChar() {

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