    @Test
    public void mergeItems() {

        Map<PrimaryKey, Item> merged = itemMapper.mergeItems(
                aggregations.stream()
                        .map(this::serialize)
                        .collect(Collectors.toList())
        );
        assertEquals(1, merged.size());
        Item mergedItem = merged.values().iterator().next();
        Aggregation aggregation1 = aggregations.get(0);
        Aggregation aggregation2 = aggregations.get(1);

        assertEquals(aggregation1.getClicks() + aggregation2.getClicks(), mergedItem.getLong("clicks"));
        assertEquals(aggregation1.getBids() + aggregation2.getBids(), mergedItem.getLong("bids"));
        assertEquals(aggregation1.getImps() + aggregation2.getImps(), mergedItem.getLong("imps"));
    }