Function read_test_db_with_download_limit 

pub fn read_test_db_with_download_limit(
    store_dir: StoreDir,
    namespace: &str,
    downloads: usize,
) -> Database

The synthetic store’s schema and Database constructors, which the database layer owns and its own tests open directly. Like read_test_db but with a chosen max_concurrent_downloads, so a pin test can drive the download loop concurrently. Uploads run one at a time (not exercised here).