Not only that, testing and burning is nice when you are testing out overburning situations. If you are attempting to overburn and you don't know if your cdr will be able to handle it then you can test and then burn if you don't get any error messages rather than burning and finding out that you've wasted a cdr and your precious time realizing that your cdr won't cut it. whew!
Of course, you have to have a burner that supports overburning and you usually have to do it DAO which means burning from HDD files whether wav or mp3, whatever. I just did a Peter Gabriel compilation on a Kodak Silver/Gold which I wasn't sure of how much space I could overburn. So, I tested a 74 min Kodak cdr with 74 mins and 54 secs worth of music and it said it was fine, burned it and it was all good.