`cargo test` should show test execution time for slower tests

[nyurik]

Problem

cargo test only prints ok/FAILED after each test. In some cases, it might be very useful to see the test duration, similar to mocha-js. Of course this is not as good as having a comprehensive benchmark tests, but in many cases it would give general feedback of how long each test took.

Proposed Solution

Print the time each test took to run in ms, either always, or just for the tests that take longer than some magic number like 10ms:

running 2 tests
test tests::test_fast ... ok
test tests::test_slow ... ok (1200ms)

Notes

Not sure if it would be worth it to introduce attributes to set the expected execution time, something like #[test(slow = 5000)] -- this would clearly be a far wider discussion.

Example from the Mocha project

[ehuss]

Thanks for the suggestion! I believe this is already implemented via the --report-time option. I'm going to close in favor of the tracking issue. For future reference, the test harness (the thing that runs the tests and prints the output) is tracked in the https://github.com/rust-lang/rust/ repository as it is not part of cargo.

[nyurik]

@ehuss thanks for the quick reply -- this is exactly what I was looking for! I so wish it was a bit more discoverable - I searched through the cargo test --help, but didn't realize some of the options were not part of that text (the cargo help test doesn't mention it either). Do you think it would be possible to somehow list all options available after the -- ?

[ehuss]

cargo help test does point out how to get the information:

For details about libtest's arguments see the output of cargo test -- --help and check out the rustc book's chapter on how tests work at https://doc.rust-lang.org/rustc/tests/index.html.

I don't think we want to replicate all of the help content (and I don't think we can with the built-in help), but I think adding a small mention to run cargo test -- --help at the bottom of cargo test --help would be good. That goes here if you'd like to post a PR.

[nyurik]

Thanks @ehuss , submitted. I wasn't too sure what to call those options - it is not very clear what those options are, as they are part of the rustc default test harness i guess.