fn create_phone_number(numbers: &[u8]) -> String {
    let numbers = numbers.iter().map(|i| i.to_string()).collect::<String>();
    format!("({}) {}-{}", &numbers[..3], &numbers[3..6], &numbers[6..])
}

#[test]
fn returns_expected() {
    assert_eq!(
        create_phone_number(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]),
        "(123) 456-7890"
    );
    assert_eq!(
        create_phone_number(&[1, 1, 1, 1, 1, 1, 1, 1, 1, 1]),
        "(111) 111-1111"
    );
    assert_eq!(
        create_phone_number(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 9]),
        "(123) 456-7899"
    );
}