Find all permutations of uppercase and lowercase characters in a string

main.rs

fn main() {
    println!("{:?}", case_permutation(String::from("ab2")));
}

pub fn case_permutation(str: String) -> Vec<String> {
    let mut permuts: Vec<String> = vec!["".to_string()];

    for c in str.chars() {
        let mut tmp = vec![];
        let lower = c.to_ascii_lowercase();
        let upper = c.to_ascii_uppercase();

        if lower == upper {
            for p in permuts.into_iter() {
                let mut copy = p.clone();
                copy.push(c);
                tmp.push(copy);
            }
        } else {
            for p in permuts.into_iter() {
                let mut low = p.clone();
                low.push(lower);
                let mut up = p.clone();
                up.push(upper);
                tmp.push(low);
                tmp.push(up);
            }
        }

        permuts = tmp;
    }

    permuts
}

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

    #[test]
    fn test_case_permutation() {
        let input = "ab2";

        assert_eq!(
            case_permutation(String::from(input)),
            vec!["ab2", "aB2", "Ab2", "AB2"]
        );

        let input = "35p";
        assert_eq!(case_permutation(String::from(input)), vec!["35p", "35P"]);

        let input = "1234";
        assert_eq!(case_permutation(String::from(input)), vec!["1234"]);

        let input = "ab";
        assert_eq!(
            case_permutation(String::from(input)),
            vec!["ab", "aB", "Ab", "AB"]
        );
    }
}