Parameterizing Unit Tests via Generic Assertion Traits

trait AssertResultExt<T, E> {
    fn assert_ok_matches<F>(self, matcher: F) where F: FnOnce(T);
}
 
impl<T, E> AssertResultExt<T, E> for Result<T, E>
where
    E: std::fmt::Debug,
{
    fn assert_ok_matches<F>(self, matcher: F)
    where
        F: FnOnce(T),
    {
        match self {
            Ok(value) => matcher(value),
            Err(err) => panic!("Expected Ok, but got Err: {:?}", err),
        }
    }
}
 
#[cfg(test)]
mod tests {
    use super::*;
 
    fn get_even_number(x: i32) -> Result<i32, String> {
        if x % 2 == 0 {
            Ok(x)
        } else {
            Err("Not even".to_string())
        }
    }
 
    #[test]
    fn test_even_logic() {
        let result = get_even_number(42);
        result.assert_ok_matches(|val| {
            assert!(val > 40);
            assert_eq!(val, 42);
        });
    }
}