dest.add("existing");

        SuggestItem.concatValues(dest, "new1", "new2", "existing");

        assertEquals(3, dest.size());
        assertTrue(dest.contains("existing"));
        assertTrue(dest.contains("new1"));
        assertTrue(dest.contains("new2"));
        // Should not have duplicate "existing"

        newUrl1.setUrl("https://example.com/new1");

        UrlQueueImpl<Long> newUrl2 = new UrlQueueImpl<>();
        newUrl2.setSessionId(sessionId);
        newUrl2.setUrl("https://example.com/new2");

        List<UrlQueueImpl<Long>> newUrlList = new ArrayList<>();
        newUrlList.add(newUrl1);
        newUrlList.add(newUrl2);

        when(dataHelper.getUrlQueueList(sessionId)).thenReturn(existingQueue);