@Override
    public int hashCode() {
        return map.hashCode();
    }
@Test
    public void testHashCode_sameHashCodeOnTheSameData() {
        ItemCounter<Object> otherCounter = new ItemCounter<>();

        int hashCode = counter.hashCode();
        int otherHashCode = otherCounter.hashCode();

        assertEquals(hashCode, otherHashCode);
    }