// Test destroy
    public void test_destroy() {
        thumbnailManager.destroy();
        assertFalse(thumbnailManager.generating);
    }

    // Test purge with expired files
    public void test_purge_withExpiredFiles() throws IOException {
        // Create test files
        File dir1 = new File(tempDir, "_1");
        dir1.mkdirs();
        File expiredFile = new File(dir1, "expired.png");