Add logs to cargo bench

Question

I'm using the criterion library to benchmark some code and am in need of printing logs via the log crate. I ran the following command on this snippet of code:

cargo bench --bench my_benchmark

warn!("Please warn");
println!("Please print");

But surprisingly found that my output looked like this:

Please print

At first when I wasn't seeing logs I figured I was missing the --nocapture flag based on a similar question asked on SO on adding logs to unit tests and the criterion docs. This had no effect. Neither did adding the RUST_LOG parameter.

# Same output as above
cargo bench --bench my_benchmark -- --nocapture

# Same output as above
RUST_LOG=debug cargo bench --bench my_benchmark

I don't know if I'm missing something obvious from a crate feature or if this is possible at all. Any help would greatly improve my time to debug. Thank you!

Answer 1

Simply add the logger initialization to each benchmark.

use log::warn; 

env_logger::builder().is_test(true).try_init().unwrap();
warn!("This prints");