Come up with a logging solution for tests.

[Yawning]

We have standardized on log as our logging library. The pretty_env_logger (or env_logger for that matter) logs to stderr, but the output file descriptor can be changed at initialization time to stdout. cargo test is supposed to capture all writes to stdout to avoid spam (cargo test -- --nocapture disables this behavior), but this is currently broken (rust-lang/rust#42474), in the context of multi-threaded code.

It would be nice to have logs that can be enabled/disabled for the tests, if only for debugging.

[Yawning]

This seems to work, and I'm using it in the ethereum random beacon test case.

fn try_init_logging() {
    // `pretty_env_logger` logs to stderr by default.  While it could be
    // re-targetted to log to stdout, Rust/Cargo bugs prevent stdout from
    // threads being captured, so there's no point.
    //
    // See: https://github.com/rust-lang/rust/issues/42474

    for arg in std::env::args() {
        if arg == "--nocapture" {
            pretty_env_logger::formatted_builder()
                .unwrap()
                .filter(None, LevelFilter::Trace)
                .init();
            return;
        }
    }
}

[pro-wh]

why should we configure it to to write to stdout?

[Yawning]

Because tests run by cargo test will squelch writes to stdout (well, it will try to, it's kind of broken) unless --nocapture is explicitly specified, in order to keep output readable. I think this is reasonable behavior because "pages and pages of web3 logs for the random beacon test" for example, aren't useful to most people unless they're debugging it.