Testing Rust Projects

Result Assertion

Check Success Paths

Result-returning helpers are easy to test by asserting that a parse succeeded before unwrapping the value.

Program

Play the program to choose numeric input and verify the success path before printing the parsed count.

result_assertion.rs 
fn main() {
    let text = ;
    let result = parse_count(text);
    assert!(result.is_ok());
    let count = result.unwrap();
    println!("{count}");
}

fn parse_count(text: &str) -> Result<i32, String> {
    text.parse::<i32>().map_err(|_| String::from("not a number"))
}

fn main() {
    let text = ;
    let result = parse_count(text);
    assert!(result.is_ok());
    let count = result.unwrap();
    println!("{count}");
}

fn parse_count(text: &str) -> Result<i32, String> {
    text.parse::<i32>().map_err(|_| String::from("not a number"))
}

fn main() {
    let text = ;
    let result = parse_count(text);
    assert!(result.is_ok());
    let count = result.unwrap();
    println!("{count}");
}

fn parse_count(text: &str) -> Result<i32, String> {
    text.parse::<i32>().map_err(|_| String::from("not a number"))
}
Result `Result<T, E>` makes success and failure explicit.
assert! `assert!(result.is_ok())` checks the success condition before unwrapping.
unwrap `unwrap` is safe here because the assertion already checked this controlled input.