---
date: 2020-09-18
id: 23e290f6-c964-4aee-a133-232291ecdba8
title: Tests in Rust
---

# Assertions

## assert!

``` rust
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))
    }
}
```

## assert~eq~!

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

# Results

## Contains

``` rust
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

## should~panic~

``` rust
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:

``` rust
#[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](https://doc.rust-lang.org/stable/book/ch11-03-test-organization.html)
for more information.

# Using Result \<T, E\> in Tests

This is possible for when you want to use the [question mark
operator](https://doc.rust-lang.org/edition-guide/rust-2018/error-handling-and-panics/the-question-mark-operator-for-easier-error-handling.html)
in your tests:

``` rust
#[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"))
        }
    }
}
```