### Question:
CharacterReader { void mark() { mark = pos; } CharacterReader(String input); @Override String toString();  }### Answer:
@Test public void mark() { CharacterReader r = new CharacterReader("one"); r.consume(); r.mark(); assertEquals('n', r.consume()); assertEquals('e', r.consume()); assertTrue(r.isEmpty()); r.rewindToMark(); assertEquals('n', r.consume()); }