Function pool_for 

pub(crate) fn pool_for(
    pools: &'static Mutex<HashMap<PathBuf, &'static Pool<SqliteConnectionManager>>>,
    path: PathBuf,
    read_only: bool,
    max_size: u32,
    migrate: Option<fn(&Connection) -> Result<()>>,
) -> Result<&'static Pool<SqliteConnectionManager>>