boolean result = thumbnailManager.offer(docMap2);
        assertTrue(result);
    }

    // Test getImageFilename with docMap
    public void test_getImageFilename_withDocMap() {
        Map<String, Object> docMap = new HashMap<>();
        docMap.put("_id", "1234567890abcdef");

        String filename = thumbnailManager.getImageFilename(docMap);
        assertNotNull(filename);