Summary - Testing

Combine unit, integration and doc tests to test a math crate.

Testing summary

Unit tests are written in src/ in a #[cfg(test)] mod tests module, also reaching private items. Integration tests in the tests/ folder use only the public API. Doc tests run the examples in /// comments. Checks: assert!, assert_eq!, assert_ne!; for an expected panic #[should_panic(expected = "..")]. Tests can also return Result<(), E>, so ? can be used.

Testing with ?

In tests whose setup steps may fail, ? is cleaner than chains of unwrap:

fn yas(s: &str) -> Result<u8, String> {
    s.trim().parse().map_err(|e| format!("geçersiz yaş: {e}"))
}

#[test]
fn yas_okunur() -> Result<(), String> {
    let y = yas(" 30 ")?;
    assert_eq!(y, 30);
    Ok(())
}

Exercise Test returning Result

Write the yas function above and the yas_okunur test returning Result<(), String>. In main, print the result of yas(" 30 ") with {:?}.

Show example solution

fn yas(s: &str) -> Result<u8, String> {
    s.trim().parse().map_err(|e| format!("geçersiz yaş: {e}"))
}

fn main() {
    println!("{:?}", yas(" 30 "));
}

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

    #[test]
    fn yas_okunur() -> Result<(), String> {
        let y = yas(" 30 ")?;
        assert_eq!(y, 30);
        Ok(())
    }
}

Test yourself

What happens if a test returning <code>Result</code> returns <code>Err</code>?
- The test counts as failed and the error is printed
- The test counts as passed
- It doesn't compile
- It's skipped
Show answer

The test counts as failed and the error is printed — #[should_panic] can't be used on tests returning Result; an expected error is written with assert!(r.is_err()).

Test return type

#[test]
fn yas_okunur() -> ____ {
    let y = yas("30")?;
    assert_eq!(y, 30);
    Ok(())
}

Show answer

#[test]
fn yas_okunur() -> Result<(), String> {
    let y = yas("30")?;
    assert_eq!(y, 30);
    Ok(())
}

Group summary

#[test]

Test function
tests/ folder

Integration test
/// ```

Doc test
#[should_panic]

Expected panic

Next lesson: Reading a file

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