this isn't quite set up the way the article was mentioning. Here's with it set up correctly:
https://play.rust-lang.org/?version=stable&mode=debug&editio...
It looks like it still misses some of the cases (specifically with decomposed vs precomposed).
As a side note, it looks like the playground editor also doesn't correctly render some of the lengths (the cursor is 1 character off on the decomposed case)