assertEquals("document", SuggestItem.Kind.DOCUMENT.toString());
        assertEquals("user", SuggestItem.Kind.USER.toString());
    }

    @Test
    public void testGetUpdatedSource() {
        // Test getUpdatedSource method
        String[] text = { "test" };
        String[][] readings = { { "test" } };
        SuggestItem item = new SuggestItem(text, readings, null, 10L, 20L, 1.0f, null, null, null, SuggestItem.Kind.QUERY);

    /**
     * Returns the updated source map by merging with existing source.
     * @param existingSource The existing source map.
     * @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.