Recursive Impl of a Subsets function

subsets.rs

fn subsets<T>(set: &[T]) -> Vec<Vec<&T>> {
    if let Some((first, rest)) = set.split_first() {
        let mut subsets = subsets(rest);
        for mut set in subsets.clone() {
            set.insert(0, first.clone());
            subsets.push(set);
        }
        subsets
    } else {
        vec![vec![]]
    }
}

#[test]
fn subsets_test() {
    let set = vec![1, 2, 3, 4];
    let res = subsets(&set);
    assert_eq!(subsets.len(), set.len().pow(2));
    println!("Subsets: {:?}", subests);
}

fn main() {
    let set = vec!['a', 'b', 'c', 'd'];
    let mut subsets = subsets(&set);
    subsets.sort_by_key(|s| s.len());
    println!("Subsets: {:?}", subsets);
    assert_eq!(subsets.len(), set.len().pow(2));
}