#![allow(dead_code, deprecated, unused_variables, unused_mut)]
fn main() {
    let s = "❤️🧡💛💚💙💜";
    assert_eq!(s.len(), 26);
    assert!(! s.is_char_boundary(13));
    let closest = s.floor_char_boundary(13);
    assert_eq!(closest, 10);
    assert_eq!(& s[..closest], "❤️🧡");
}