I tried the practices, and I didn't like it because they don't provide sample input, and you can't test your changes in browser. Most of my seconds are spent copying and pasting, and setting up sample input. I guess other people are more perfect typists, but I make typos and so my solutions were often wrong if I didn't test them.
I don't think testing would be of much help. These challenges are so designed that there is precisely one error in the function and precisely one way to fix it and either you notice it or you don't. If you were able to test your changes on the fly you could just as well try all the different modifications you can think of (of which there aren't many) without thinking too much.
