@Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        ItemCounter that = (ItemCounter) o;
        if (!map.equals(that.map)) {
            return false;
        }
        return true;
    }
@Test
    public void testEquals_returnsFalseOnNull() {
        assertFalse(counter.equals(null));
    }