Suggest `--ignored` when libtest ignores a test

[jyn514]

Code

; cat src/lib.rs
#[test]
#[ignore = "takes too long 😩"]
fn i_am_slow() {
    std::thread::sleep(std::time::Duration::from_secs(5));
    println!("it works!");
}
; cargo test --lib --quiet

Current output

running 1 test
i
test result: ok. 0 passed; 0 failed; 1 ignored; 0 measured; 0 filtered out; finished in 0.00s

test: i_am_slow, ignore_message: takes too long 😩

Desired output

running 1 test
i
test result: ok. 0 passed; 0 failed; 1 ignored; 0 measured; 0 filtered out; finished in 0.00s

test: i_am_slow, ignore_message: takes too long 😩

note: to run ignored tests, use `--ignored`

Rationale and extra context

See rust-lang/cargo#12494; currently this will be confusing for people using cargo so I'd like to fix that issue first.

Other cases

If no tests are ignored, this help message shouldn't be printed.

Anything else?

No response

[RickleAndMortimer]

@rustbot claim

[epage]

T-testng-devex is looking at shifting the responsibilities for test reporting from libtest to cargo test, leveraging the json output. In the long run, we'd then want something like this in cargo test. My main question would be how to present this without annoying the user when they always have an ignored test. For them, it bloats the output and becomes something that gets ignored. It could be like git where there are user messages that are on by default and can individually be turned off via config.