$ cargo test Compiling limit-tracker v0.1.0 (file:///projects/limit-tracker) Finished test [unoptimized + debuginfo] target(s) in 0.91s Running unittests src/lib.rs (target/debug/deps/limit_tracker-e599811fa246dbde) running 1 test test tests::it_sends_an_over_75_percent_warning_message ... FAILED failures: ---- tests::it_sends_an_over_75_percent_warning_message stdout ---- thread 'main' panicked at 'already borrowed: BorrowMutError', src/lib.rs:60:53 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace failures: tests::it_sends_an_over_75_percent_warning_message test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s error: test failed, to rerun pass `--lib`