with_test_writer() doesn't work in unit tests

[realtica]

Hello, I do not know why Tracing only fails inside unit tests, here is my config:

tracing = "0.1.37"
time = "0.3.29"
tracing-subscriber = {version = "0.3.17", features = ["env-filter", "fmt", "ansi", "std", "time"] }

    let time_format = time::format_description::parse("[hour]:[minute]:[second]")
        .expect("format string should be valid!");
    let timer = UtcTime::new(time_format);
    let format = fmt::format()
        .with_line_number(true)
        // .with_source_location(true)
        .with_timer(timer)
        .with_level(true) // don't include levels in formatted output
        .with_target(false) // don't include targets
        .with_thread_ids(false) // include the thread ID of the current thread
        .with_thread_names(false) // include the name of the current thread
        .pretty(); // use the `Compact` formatting style.
    tracing_subscriber::fmt()
        .with_test_writer()
        .event_format(format)
        .init();

[hawkw]

You are calling the fmt::Subscriber::init() method, which panics if it is called more than once, as discussed in the documentation. Since multiple unit tests will run in the same binary, each test that calls into your tracing setup code will call init(), and any subsequent calls to init() after the first will panic. You can fix this by using try_init() rather than init() --- this method returns a Result if the global default subscriber has already been initialized. In tests, you can simply ignore the Result this method returns.

Hope that helps!

[realtica]

Not showing any log in unit tests yet, I also added tracing-log feature too.

let _ = tracing_subscriber::fmt()
        .with_test_writer()
        .event_format(format)
        .try_init();

tracing-subscriber = {version = "0.3.17", features = ["env-filter", "fmt", "ansi", "std", "time", "tracing-log"] }

❯ cargo test
   Compiling rapidsite v0.0.1 (/home/realtica/projects/rapidsite/src-tauri)
    Finished test [unoptimized + debuginfo] target(s) in 6.20s
     Running unittests src/main.rs (target/debug/deps/rapidsite-91a95a5b19e1c261)

running 2 tests
test app::file_management::tests::get_folder_list_test ... ok
test app::file_management::tests::get_file_list_test ... ok

test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

[hawkw]

This is normal. By default, Rust tests capture all output from the test and only display it if the test fails. If you want to see output from passing tests, run your tests using

cargo test -- --show-output