Another useful attribute for writing tests is #[ignore]. If your test code is exceedingly heavy, the #[ignore] annotation enables the test harness to ignore such test functions when running cargo test. You can then choose to individually run those tests by supplying an --ignored parameter to either your test runner or the cargo test command. Here's the code containing a silly loop that, when run using cargo test, is ignored by default:

// silly_loop.rs

pub fn silly_loop() {
    for _ in 1..1_000_000_000 {};
}

#[cfg(test)]
mod tests {
    #[test]
    #[ignore]
    pub fn test_silly_loop() {
        ::silly_loop();
    }
}

Note the #[ignore] attribute over the test_silly_loop test function. Here's the output from the ignored test: