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

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

    // helper function for tests
    fn assert_add(a: i32, b: i32, expected: i32) {
        assert_eq!(add(a, b), expected, "add({}, {}) should be {}", a, b, expected);
    }

    mod add_tests {
        use super::*;

        #[test]
        fn positive() { assert_add(2, 3, 5); }

        #[test]
        fn negative() { assert_add(-1, -2, -3); }

        #[test]
        fn zero() { assert_add(0, 0, 0); }
    }

    mod mul_tests {
        use super::*;

        #[test]
        fn basic() { assert_eq!(mul(3, 4), 12); }

        #[test]
        fn identity() { assert_eq!(mul(5, 1), 5); }
    }
}

fn main() {
    println!("Run with: cargo test");
}