@Test
public void testPeek() {

  assertParser(mode, INTEGER.peek(), "12", 12, "12");
  assertFailure(mode, INTEGER.peek(), "a", 1, 1);
  assertFailure(mode, areChars("ab").peek(), "a", 1, 2);
  assertParser(mode, Parsers.or(areChars("ab").peek(), isChar('a')), "a", 'a', "");
  assertEquals("peek", INTEGER.peek().toString());
}