    @Test
    public void testKeysReleased2() throws Exception {

        ks1 = new KeyboardState(EnumSet.of(Key.A, Key.B), KeyEvent.NOTHING);
        ks2 = new KeyboardState(EnumSet.noneOf(Key.class), KeyEvent.NOTHING);

        final EnumSet<Key> released = ks2.getKeysReleasedSince(ks1);

        assertEquals("2 key", 2, released.size());
        assertTrue("a released", released.contains(Key.A));
        assertTrue("b released", released.contains(Key.B));
    }