@Test
public void testSequence_2Parsers() {

  Parser<Void> parser = Parsers.sequence(Scanners.isChar('a'), Scanners.isChar('b'));
  assertEquals("sequence", parser.toString());
  assertEquals(null, parser.parse("ab", mode));
  assertFailure(mode, parser, "xb", 1, 1);
  assertFailure(mode, parser, "ax", 1, 2);
}