为什么货物测试显示我的踪迹！ 当我指定 RUST_LOG=debug?

Question

Why does cargo test show me trace! logs when I specify RUST_LOG=debug ?

I'm using SimpleLogger as a test backend, initialized like that ( init_logger is called at the beginning of each test function):

static INIT_LOGGER: Once = Once::new();

pub fn init_logger() {
    INIT_LOGGER.call_once(|| {
        SimpleLogger::new().init().unwrap();
    });
}

I run the tests with:

RUST_LOG=debug cargo test

And I see all log messages, INFO , DEBUG ...

I'd like to see only the DEBUG messages.

Also, I'd like to see only the messages from my own crate, not from its dependencies, is that possible?

Answer 1

SimpleLogger by default does not react to environment variables.

Use the .env() method to enable that behaviour:

use std::sync::Once;

use simple_logger::SimpleLogger;

static INIT_LOGGER: Once = Once::new();
pub fn init_logger() {
    INIT_LOGGER.call_once(|| {
        SimpleLogger::new().env().init().unwrap();
    });
}

fn main() {
    init_logger();
    log::error!("error");
    log::warn!("warn");
    log::info!("info");
    log::debug!("debug");
    log::trace!("trace");
}

> RUST_LOG=debug cargo run
2022-07-09T14:49:19.733Z ERROR [streamer] error
2022-07-09T14:49:19.733Z WARN [streamer] warn
2022-07-09T14:49:19.733Z INFO [streamer] info
2022-07-09T14:49:19.733Z DEBUG [streamer] debug

> RUST_LOG=info cargo run
2022-07-09T14:49:25.022Z ERROR [streamer] error
2022-07-09T14:49:25.022Z WARN [streamer] warn
2022-07-09T14:49:25.022Z INFO [streamer] info

Or use the much more popular EnvLogger instead.

With EnvLogger you can do exactly what you were asking for; you can enable different log levels for different dependencies. Here is a more detailed description of what can be achieved with EnvLogger .

use std::sync::Once;

static INIT_LOGGER: Once = Once::new();
pub fn init_logger() {
    INIT_LOGGER.call_once(|| {
        env_logger::init();
    });
}

fn main() {
    init_logger();
    log::error!("error");
    log::warn!("warn");
    log::info!("info");
    log::debug!("debug");
    log::trace!("trace");
}

> RUST_LOG=debug cargo run
[2022-07-09T14:52:42Z ERROR streamer] error
[2022-07-09T14:52:42Z WARN  streamer] warn
[2022-07-09T14:52:42Z INFO  streamer] info
[2022-07-09T14:52:42Z DEBUG streamer] debug

> RUST_LOG=info cargo run
[2022-07-09T14:52:46Z ERROR streamer] error
[2022-07-09T14:52:46Z WARN  streamer] warn
[2022-07-09T14:52:46Z INFO  streamer] info