libtest - capture stderr from tests

[NoraCodes]

I'm currently having a problem with testing libraries that use log with either env_logger or flexi_logger in their tests. In the "real world", they should log to stderr, but libtest (and, by extension Cargo) doesn't capture stderr from tests, so I have to jump through hoops to get these libraries to log to stdout instead, or sift through huge logdumps.

Would it be possible to capture stderr from tests?

I originally posted this on the Cargo repo, but was told to file here. Possibly related to #31983, but I've tried limiting the test threads (RUST_TEST_THREADS=1) with no result.

[martinlindhe]

I agree on this.

For a little more detail;

Consider the following

#[macro_use]
extern crate log;

fn do_stuff() -> bool {
    println!("println");
    error!("error");
    true
}

#[test]
fn my_test() {
    assert_eq!(true, do_stuff());
}

run: cargo test -- --nocapture

actual output:

running 1 test
println
test my_test ... ok

expected output:

running 1 test
println
error
test my_test ... ok

[dpc]

Using slog-envlogger (and other slog crates) one can easily have a logger that logs to stderr, stdout, file... whatever, with colors, in one of several format and if combine it with control of RUST_LOG variable. Just saying...

[martinlindhe]

@dpc Not sure it would help, since it seems cargo test, even with the --nocapture swallows stderr. Only stdout is shown.

[dpc]

@ martinlindhe ... Edited my original coment. Slog doesn't care. Log to stdout, stderr, file. Or even open new raw 1 file descriptor and circumvent cargo test jail.

[dpc]

I actually should create slog-test crate specifically for that purpose... Ping me on slog gitter if you're interested. I guess it's enough of slog advertising. :D

[martinlindhe]

@dpc, Okay.. so I can make a custom slog logger that outputs to stdout, thus allow cargo test to fetch the output. Gotcha.
Will also checkout slog when time permits!
But I think it would benefit the end user more if cargo test would display stderr, even if it is hidden behind a rather obscure flag as --nocapture.
Especially considering the log crate is the default logger as documented on rust-lang.org

[NoraCodes]

Yes, I agree. Not everyone is in a position to use slog, as awesome as it is.

…

On Fri, Mar 31, 2017, 15:36 Martin Lindhe ***@***.***> wrote: @dpc <https://github.com/dpc>, Okay.. so I can make a custom slog logger that outputs to stdout, thus allow cargo test to fetch the output. Gotcha. But I think it would benefit the end user more if cargo test would display stderr, even if it is hidden behind a rather obscure flag as --nocapture. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#40298 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ADI0_dspanD5UUkSfN3CQYGj7A2WUYXLks5rrWPbgaJpZM4MUXd0> .