Rust test module and test function to unit test a function.

main.rs

#[cfg(test)]
mod test_mod {

    use super::divide; // Importing the divide function from the outer scope.

    #[test]
    fn test_divide_2_values() {
        let result1 = divide(4.0, 2.0); // Calling the divide function with arguments 4.0 and 2.0 and storing the result in result1.

        assert_eq!(result1, Result::Ok(2.0)); // Asserting that the value of result1 is equal to an Ok variant of the Result enum with a value of 2.0.
    }

    #[test]
    fn test_divide_by_zero() {
        let result1 = divide(4.0, 0.0); // Calling the divide function with arguments 4.0 and 0.0 and storing the result in result1.

        assert_eq!(
            result1,
            Result::Err("Hey, you can't divide by zero".to_string()) // Asserting that the value of result1 is equal to an Err variant of the Result enum with an error message.
        )
    }
}