Testing

Tests live in the same file as the code they exercise, gated behind #[cfg(test)] so they vanish from release builds. cargo test finds them, compiles them, runs them, prints results. No separate harness, no CMake variant, no fixture wiring.

A test module sits in the same file. #[cfg(test)] strips it from non-test builds. use super::* pulls the parent module's items into scope so the test can name the type without re-importing.

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn basics() {
        let mut list = List::new();
        assert_eq!(list.pop(), None);

        list.push(1);
        list.push(2);
        list.push(3);
        assert_eq!(list.pop(), Some(3));
        assert_eq!(list.pop(), Some(2));

        list.push(4);
        list.push(5);
        assert_eq!(list.pop(), Some(5));
        assert_eq!(list.pop(), Some(4));
        assert_eq!(list.pop(), Some(1));
        assert_eq!(list.pop(), None);
    }
}

cargo test runs every #[test] in parallel by default. Each test gets its own thread; failures don't cross-contaminate. --nocapture if you want to see println! from passing tests.

$ cargo test
   Compiling lists v0.1.0
    Finished test [unoptimized + debuginfo] target(s) in 0.42s
     Running unittests src/lib.rs

running 1 test
test first::tests::basics ... ok

test result: ok. 1 passed; 0 failed