    @Test
    public void hasUserInput() {

        assertFalse(mask.hasUserInput());

        mask.insertFront("1");
        assertTrue(mask.hasUserInput());

        mask.removeBackwards(0, 1);
        assertFalse(mask.hasUserInput());

        Mask nullMask = new MaskImpl(new Slot[]{}, true);
        assertFalse(nullMask.hasUserInput());
    }