Rust Testing

Reproducible testing is important for reliable software development. Rust has a powerful built-in testing features, so that test can be writting under the test modules, and invoked by cargo test. For more details, see rust doc. This blogs will focus on some convenient use cases.

How to Write Tests.

fn plus_one(x: i32) -> i32 {
    x + 1
}

fn main() {
}

#[cfg(test)]
mod tests{
    #[test]
    fn it_works() {
        assert_eq!(2, super::plus_one(1));
    }
}

And fire the test with cargo test.

Note println! will not print anything in cargo test. In the case when test by printing is favourable, run

cargo test -- --nocapture  # -- denotes the beginning of flags

Sometimes there may be thousands of tests in a crate. Passing arguments to cargo test <args> tells cargo to only run test functions whose name contains <args>. Note, the name of any parent module is also part of the name of the test function. (The above test fuction has name test::it_works.)

cargo test works  # only run test function whose name contains works.