assertNotNull(filename);
        assertTrue(filename.endsWith(".jpg"));
        assertTrue(filename.contains(docid));
    }

    // Test getThumbnailFile with existing file
    public void test_getThumbnailFile_exists() throws IOException {
        Map<String, Object> docMap = new HashMap<>();
        docMap.put("_id", "testdoc");

        String filename = thumbnailManager.getImageFilename(docMap);