assertTrue(filename.endsWith(".png"));
        assertTrue(filename.contains("/"));
    }

    // Test getImageFilename with docid - use the String version directly
    public void test_getImageFilename_withDocId() {
        String docid = "1234567890abcdef";
        // Call the String version directly
        String filename = thumbnailManager.getImageFilename(docid);
        assertNotNull(filename);