How to build test transactions

[feliwir]

Hey, how can i build a database pool that doesn't commit any operations performed on it? In regular diesel i could do this:

pub type DbConn = PgConnection;
pub type DbPool = r2d2::Pool<ConnectionManager<DbConn>>;

pub fn initialize_test_pool(database_url: &str) -> Result<DbPool, Box<dyn Error>> {
    let manager = r2d2::ConnectionManager::<DbConn>::new(database_url);
    let pool = r2d2::Pool::builder()
        .test_on_check_out(true)
        .max_size(1)
        .connection_customizer(Box::new(TestCustomizer))
        .build(manager)?;

    Ok(pool)
}

I tried using a ManagerConfig and customize the connection establishing:

pub type DbConn = AsyncPgConnection;
pub type DbPool = Pool<diesel_async::AsyncPgConnection>;


fn establish_test_connection(
    url: &str,
) -> BoxFuture<ConnectionResult<DbConn>> {
    let fut = async {
        DbConn::establish(url)
            .await
            .map_err(|e| ConnectionError::BadConnection(e.to_string()))
    };
    fut.boxed()
}

pub async fn init_test_database(url: &str) -> std::io::Result<DbPool> {
    let conn = establish_connection(url).await?;
    run_migrations(conn).await?;

    let mut config = ManagerConfig::default();
    config.custom_setup = Box::new(establish_test_connection);
    let db_config = AsyncDieselConnectionManager::<DbConn>::new_with_config(url, config);
    let pool = Pool::builder(db_config).build().map_err(|e| {
        error!("Failed to create database connection pool: {}", e);
        std::io::ErrorKind::Other
    })?;

    Ok(pool)
}

However i'm lost how to wrap the connection into a test transaction. Does someone have a solution for this kind of problem?
Thanks a lot

[weiznich]

You need to do just call AsyncConnection::begin_test_transaction in your establish_test_connection

The TestCustomizer does nothing else internally.

That written I'm open to accept a PR that adds a similar construct to the pools provided by diesel-async to make this more discoverable.