*
     * @param item The SuggestItem with new data
     * @param existingSource The existing source map from OpenSearch
     * @return A merged source map
     */
    public static Map<String, Object> toUpdatedSource(final SuggestItem item, final Map<String, Object> existingSource) {
        final Map<String, Object> map = new HashMap<>();
        map.put(FieldNames.TEXT, item.getText());

        existing.put(FieldNames.QUERY_FREQ, 3L);
        existing.put(FieldNames.TIMESTAMP, System.currentTimeMillis());

        Map<String, Object> updated = SuggestItemSerializer.toUpdatedSource(item, existing);

        assertNotNull(updated);
        assertTrue(updated.containsKey(FieldNames.DOC_FREQ));
        assertTrue(updated.containsKey(FieldNames.QUERY_FREQ));
    }

    @Test

     * @return The updated source map.
     */
    public Map<String, Object> getUpdatedSource(final Map<String, Object> existingSource) {
        return SuggestItemSerializer.toUpdatedSource(this, existingSource);
    }

    /**
     * Concatenates values to a destination list, avoiding duplicates.
     * @param dest The destination list.
     * @param newValues The new values to add.