* @return The merged suggest item.
     */
    public static SuggestItem merge(final SuggestItem item1, final SuggestItem item2) {
        if (!item1.getId().equals(item2.getId())) {
            throw new IllegalArgumentException("Item id is mismatch.");
        }

        final SuggestItem mergedItem = new SuggestItem();

        mergedItem.id = item1.getId();
        mergedItem.text = item1.getText();

        SuggestItem suggestItem = elevateWord.toSuggestItem();

        assertNotNull(suggestItem);
        assertEquals(word, suggestItem.getText());
        assertEquals(boost, suggestItem.getUserBoost(), 0.001f);
        // The queryFreq and docFreq might be handled differently by SuggestItem
        assertTrue(suggestItem.getQueryFreq() >= 0);

        words.add("test");

        List<SuggestItem> items = new ArrayList<>();
        String[][] readings = new String[1][];
        readings[0] = new String[] { "test" };
        items.add(new SuggestItem(new String[] { "test" }, readings, new String[] { "content" }, 1, 0, -1, new String[] { "tag1" },
                new String[] { SuggestConstants.DEFAULT_ROLE }, null, SuggestItem.Kind.DOCUMENT));

        SuggestItem[] items = new SuggestItem[1];
        String[][] readings = new String[1][];
        readings[0] = new String[] { "test" };
        items[0] = new SuggestItem(new String[] { "test" }, readings, new String[] { "content" }, 0, 15, -1, new String[] { "tag1" },
                new String[] { SuggestConstants.DEFAULT_ROLE }, new String[] { "en" }, SuggestItem.Kind.QUERY);

                items.add(new SuggestItem(words, readings, new String[] { field }, 0, 1, -1, tags, roles, null, SuggestItem.Kind.QUERY));
            }
        } catch (final IOException e) {
            throw new SuggesterException("Failed to create SuggestItem from query log.", e);
        }

        return items;
    }

    @Override

        SuggestItem item3 = new SuggestItem(new String[] { "テスト" }, readings, new String[] { "content" }, 3, 0, -1, new String[] { "tag1" },
                new String[] { SuggestConstants.DEFAULT_ROLE }, null, SuggestItem.Kind.DOCUMENT);
        SuggestItem item4 = new SuggestItem(new String[] { "テスト" }, readings, new String[] { "content" }, 4, 0, -1, new String[] { "tag1" },

        readings3[0] = new String[] { "both" };
        items[2] = new SuggestItem(new String[] { "両方" }, readings3, new String[] { "content" }, 1L, 1L, -1.0f, new String[] { "tag1" },
                new String[] { SuggestConstants.DEFAULT_ROLE }, null, SuggestItem.Kind.DOCUMENT);
        items[2].setKinds(new SuggestItem.Kind[] { SuggestItem.Kind.DOCUMENT, SuggestItem.Kind.QUERY });

        suggester.indexer().index(items);

     */
    public SuggestIndexResponse index(final SuggestItem item) {
        return index(new SuggestItem[] { item });
    }

    /**
     * Indexes multiple suggest items.
     * @param items The suggest items to index.
     * @return The SuggestIndexResponse.
     */
    public SuggestIndexResponse index(final SuggestItem[] items) {

    }

    @Test
    public void testConcatKinds() {
        // Test static concatKinds method
        SuggestItem.Kind[] kinds1 = { SuggestItem.Kind.QUERY };
        SuggestItem.Kind[] kinds2 = { SuggestItem.Kind.DOCUMENT, SuggestItem.Kind.QUERY };

        SuggestItem.Kind[] result = SuggestItem.concatKinds(kinds1, kinds2);

        assertNotNull(result);

     */
    default SuggestItem[] mergeItems(final SuggestItem[] items) {
        final Set<String> mergedIdSet = new HashSet<>();
        final List<SuggestItem> mergedList = new ArrayList<>(items.length);

        for (final SuggestItem item1 : items) {
            final String item1Id = item1.getId();
            if (mergedIdSet.contains(item1Id)) {
                continue;
            }

            SuggestItem mergedItem = item1;