Test

// src/lib.rs
#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}

impl Rectangle {
    fn can_hold(&self, other: &Rectangle) -> bool {
        self.width > other.width && self.height > other.height
    }
}

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

    #[test]
    fn it_works() -> Result<(), String> {
        if 2 + 2 == 4 {
            Ok(())
        } else {
            Err(String::from("Plus result is not four"))
        }
    }

    #[test]
    fn test_can_hold() {
        let r1 = Rectangle {width: 8, height: 7};
        let r2 = Rectangle {width: 5, height: 1};
        assert!(r1.can_hold(&r2));
        assert!(!r2.can_hold(&r1));
    }
}

Unit test

• Use #[cfg(test)] to annotate the mod, then it won't be run in cargo build.
• Ussually use tests as the module name.

Integration test

• Put all the tests in the folder tests. No need to add #[cfg(test)].

Cargo test

# stop hiding output
cargo test -- --nocapture