Test Runners

Recipe	Crates	Categories
Test your code with cargo test
Test your code Faster with cargo nextest

Test your code with cargo test

cargo test to run all tests. cargo test test_prefix to run all tests that start with the provided prefix. cargo test -- --show-output to show output (println!) that is otherwise captured during tests.

struct Rectangle {
    width: u32,
    height: u32,
}

impl Rectangle {
    fn can_hold(&self, _another: &Rectangle) -> bool {
        true
    }
}

// Put unit tests in the same file than the main code

#[cfg(test)] // only for unit tests
mod tests {
    // Access to all objects in the parent module,
    // which contains the main code
    use super::*;

    // Test functions must be free, monomorphic functions that take no
    // arguments, and commonly return () or Result<T, E> where T:
    // Termination, E: Debug

    #[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));
        // You may also use: assert_eq!(result, some_const);
        // or assert_ne!(...)
    }

    // This test passes if the code inside the function panics;
    // It fails if the code inside the function doesn't panic.

    #[should_panic]
    #[test]
    fn another() {
        panic!("Make this test fail");
    }

    // With Result

    #[test]
    fn it_works() -> Result<(), String> {
        if 2 + 2 == 4 {
            Ok(()) // Pass if OK
        } else {
            Err(String::from("two plus two does not equal four"))
        }
    }

    #[ignore = "This test takes an hour to run. Only run it manually when needed"]
    #[test]
    fn expensive_test() {
        // Long-running code
    }
}

Test your code Faster with cargo nextest

cargo-nextest⮳ is a new, faster test runner for Rust.

cargo nextest run
cargo test --doc