#learn-rust: tests

Syntax to write tests in Rust:

fn add(a: i32, b: i32) -> i32 {
    a + b
}

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

    #[test]
    fn add_works() {
        assert_eq!(add(1, 2), 3);
        assert_eq!(add(10, 12), 22);
        assert_eq!(add(5, -2), 3);
    }

    #[test]
    #[should_panic]
    fn add_fails() {
        assert_eq!(add(2, 2), 7);
    }

    #[test]
    #[ignore]
    fn add_negatives() {
        assert_eq!(add(-2, -2), -4)
    }
}

The cfg attribute controls conditional compilation and will only compile the thing it’s attached to if the predicate is true. The test compilation flag is issued automatically by Cargo whenever we execute the command $ cargo test, so it will always be true when we run our tests. The use super::*; declaration is necessary for the code inside the add_function_tests module to access the add in the outer module.