Tests in Rust

Assertions

assert!

struct Rectangle {
    width: u32,
    height: u32,
}
 
impl Rectangle {
    pub fn can_hold(&self, other: &Rectangle) -> bool {
        self.width > other.width && self.height > other.height
    }
}
 
pub struct Guess {
    value: i32,
}
 
#[cfg(test)]
mod tests {
    use super::*;
 
    #[test]
    fn larger_can_hold_smaller() {
        let larger = Rectangle {
            width: 8,
            height: 7,
        };
        let smaller = Rectangle {
            width: 5,
            height: 1,
        };
 
        assert!(larger.can_hold(&smaller))
    }
 
    #[test]
    fn smaller_cannot_hold_larger() {
        let larger = Rectangle {
            width: 8,
            height: 7,
        };
        let smaller = Rectangle {
            width: 5,
            height: 1,
        };
 
        assert!(!smaller.can_hold(&larger))
    }
}

asserteq!

#[cfg(test)]
mod tests {
    #[test]
    fn it_works() {
        assert_eq!(2 + 2, 4);
    }
}

Results

Contains

pub fn greeting(name: &str) -> String {
    format!("Hello {}!", name)
}
 
#[cfg(test)]
mod tests {
    use super::*;
 
    #[test]
    fn greeting_contains_name() {
        let result = greeting("Carrol");
        assert!(
            result.contains("Carrol"),
            "Greeting did not countain name, value was `{}`",
            result
        )
    }
}

Annotations

shouldpanic

pub struct Guess {
    value: i32,
}
 
impl Guess {
    pub fn new(value: i32) -> Guess {
        if value < 1 {
            panic!(
                "Guess value must be greater than or equal to 1, got {}.",
                value
            );
        } else if value > 100 {
            panic!(
                "Guess value must be less than or equal to 100, got {}.",
                value
            );
        }
 
        Guess { value }
    }
}
 
#[cfg(test)]
mod tests {
    use super::*;
 
    #[test]
    #[should_panic(expected = "Guess value must be less than or equal to 100")]
    fn greater_than_100() {
        Guess::new(200);
    }
}
 

ignore

This ignores tests unless specifically requested:

#[test]
#[ignore]
fn expensive_test() {
    // code that takes an hour to run
}
 
fn main() {}

Integreation Tests

Integration tests are their own thing and I’m too lazy to take notes now as it’s 18:59 on a Friday. See relevant chapter in the book for more information.

Using Result <T, E> in Tests

This is possible for when you want to use the question mark operator in your tests:

#[cfg(test)]
mod tests {
    use super::*;
 
    #[test]
    fn it_works() -> Result<(), String> {
        if 2 + 2 == 4 {
            Ok(())
        } else {
            Err(String::from("two plus two does not equal four"))
        }
    }
}