@DoNotSub private static int next(final int index, final int mask)
    {
        return (index + 2) & mask;
    }
@Test
    void shouldExceptionWhenRunningOutOfElements()
    {
        addTwoElements();

        final Iterator<Integer> iterator = keyIterator();
        iterator.next();
        iterator.next();

        assertThrows(NoSuchElementException.class, iterator::next);
    }