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Calculator with Unit Tests (Rust)

This example shows:

• functions (add, sub, mul, div)
• using panic! for invalid input
• unit tests with #[test]
• #[should_panic] and #[ignore]

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fn add(a: f32, b: f32) -> f32 {
    a + b
}

fn sub(a: f32, b: f32) -> f32 {
    if a < b {
        panic!("first value cannot be less than the second value");
    } else {
        a - b
    }
}

#[allow(dead_code)]
fn mul(a: f32, b: f32) -> f32 {
    a * b
}

#[allow(dead_code)]
fn div(a: f32, b: f32) -> f32 {
    a / b
}

fn main() {
    let a: f32 = 17.0;
    let b: f32 = 33.0;
    let op = "-";

    let result = if op == "+" {
        add(a, b)
    } else if op == "-" {
        sub(a, b)
    } else if op == "*" {
        mul(a, b)
    } else if op == "/" {
        div(a, b)
    } else {
        panic!("unsupported operator: {op}");
    };

    println!("{result}");
}


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

    #[test]
    fn test_add() {
        assert_eq!(add(20.0, 10.0), 30.0);
        assert_eq!(add(10.0, 20.0), 30.0);
        result = add(1.0,2.0);
        assert_eq!(result,4,"Expected 3; returned result is {}", result);
    }

    #[test]
    #[should_panic(expected = "cannot be less")]
    fn test_sub_panics_when_a_less_than_b() {
        sub(10.0, 20.0);
    }

    #[test]
    fn test_sub_ok() {
        assert_eq!(sub(20.0, 10.0), 10.0);
    }

    #[test]
    #[ignore]
    fn test_sub_ignored_example() {
        assert_eq!(sub(20.0, 10.0), 10.0);
    }
}

Other variations of asserts

• assert!
• assert_eq!
• assert_ne!

Run the script

cargo run

Run all tests

cargo test

Run ignored tests too

cargo test -- --ignored

Run specific test

cargo run sub

Show println output during tests

cargo test -- --nocapture

Run tests in specific thread

By default Rust uses multiple threads for speed.

cargo test -- --test-threads=1

Additional Links:

• Rust book testing chapter: https://doc.rust-lang.org/book/ch11-01-writing-tests.html
• cargo test options: https://doc.rust-lang.org/cargo/commands/cargo-test.html

#calculator #unittestVer 2.0.7