public void incrementCount() {
        incrementCount(headSlot, 1);
    }
@Test
    public void testIncrementCount() {
        assertEquals(0, counter.get(1));
        assertEquals(0, counter.get(2));
        counter.incrementCount();
        assertEquals(1, counter.get(1));
        assertEquals(1, counter.get(2));
        counter.incrementCount(2);
        assertEquals(3, counter.get(2));
    }