The std::str::Chars iterator has a nice Debug output:

fn main() {
    let mut chars = "abc".chars();
    println!("{:?}", chars);
    chars.next();
    println!("{:?}", chars);
}

produces:

Chars(['a', 'b', 'c'])
Chars(['b', 'c'])

It would be nice to see unicode_segmentation::Graphemes and so forth implement a nice Debug output to display what they're going to be producing in the future.