I'm writing tests for a Rust program that uses the tracing crate for logging, and the test-log crate to enable logging in the tests.

I have an arrange step that does quite a lot of things, which I want to log at the "info" level.

I want logging for the act step to be at "debug" level, so I can get useful logs in the test output, but only for the act step.

How can this be achieved?

Some things I tried:

// This works, but sets the level globally
#[tokio::test]
async fn test_dynamic_logging1() {
    use tracing_subscriber::{ filter, fmt, reload, prelude::* };
    let filter = filter::LevelFilter::INFO;
    let (filter, reload_handle) = reload::Layer::new(filter);
    tracing_subscriber::registry().with(filter).with(fmt::Layer::default()).init();
    info!("This will be logged");
    debug!("This will be ignored");
    reload_handle
        .modify(|filter| {
            *filter = filter::LevelFilter::DEBUG;
        })
        .unwrap();
    debug!("This will be logged");
}

// This doesn't work
#[tokio::test]
async fn test_dynamic_logging2() {
    use tracing_subscriber::{ filter, fmt, reload, prelude::* };
    let filter = filter::LevelFilter::INFO;
    let (filter, reload_handle) = reload::Layer::new(filter);
    tracing_subscriber::registry().with(filter).with(fmt::Layer::default()).init();

    info!("This will be logged");
    debug!("This will be ignored");

    let debug_subscriber = fmt::Subscriber
        ::builder()
        .with_max_level(tracing::Level::DEBUG)
        .with_test_writer()
        .finish();
    tracing::subscriber::with_default(debug_subscriber, || {
        debug!("This should be logged, but isn't");
    });
    info!("This will be logged");
    debug!("This will be ignored");
}

A few minutes after posting this, I got it to work for test-log as well:

    #[test_log::test(tokio::test)]
    async fn test_dynamic_logging3() {
        debug!("This will be ignored");

        let debug_subscriber = tracing_subscriber::fmt::Subscriber
            ::builder()
            .with_max_level(tracing::Level::DEBUG)
            .with_test_writer()
            .finish();
        tracing::subscriber::with_default(debug_subscriber, || {
            debug!("This will be logged");
        });
        debug!("This will be ignored");
    }

But in the real test, the code is async, and when I change it to this, the line isn't logged anymore:

        tracing::subscriber::with_default(debug_subscriber, || async {
            debug!("This will be logged");
        }).await;