fn main() {
    println!();

    let mut str = ('a'..='z').collect::<String>();
    let bad = ('n'..='z').collect::<String>();
    let rng: Vec<_> = ('n'..='z').collect();
    let err: &[_] = &&rng;
    let sls = "";
    let st2 = "kkkwwwaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbmmmmmmmmmmmmmmmmmmmxyz";

    println!("{:?}\t{:?}\t{:?}\t{:?}",
        func(&str),
        &str.trim_matches(err),
        str.len(),
        sls
    );

    println!("\n{:?}\n{:?}\t{:?}:{:?}",
        st2,
        st2.chars().filter(|&c| err.contains(&c)).collect::<String>(),
        st2.chars().filter(|&c| "nopqrstuvwxyz".contains(c)).count(),
        st2.len()
    );

    println!("\n{:?}\n{:?}\t{:?}:{:?}",
        st2,
        st2.chars().filter(|&c| c > 'm').collect::<String>(),
        st2.chars().filter(|&c| c > 'm').count(),
        st2.len()
    );

    println!("\n{:?}\t{:?}",
        str,
        str.chars().filter(|&c| err.contains(&c)).collect::<String>(),
    );

    println!();
}

fn func(s: &str) -> String {
    s.into()
}
fn printer_error(s: &str) -> String {
    format!("{}/{}",
        s.chars().filter(|&c| "nopqrstuvwxyz".contains(c)).count(),
        s.len()
    )
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn should_pass_all_the_tests_provided() {
        assert_eq!(&printer_error("aaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbmmmmmmmmmmmmmmmmmmmxyz"), "3/56");
        assert_eq!(&printer_error("kkkwwwaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbmmmmmmmmmmmmmmmmmmmxyz"), "6/60");
        assert_eq!(&printer_error("kkkwwwaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbmmmmmmmmmmmmmmmmmmmxyzuuuuu"), "11/65");
    }
}