Snce testcd is intended to test a CD, you're not doing yourself any favor here.

If you have a CD and want to test it, I suggest the testcd parameter without the bootfrom=iso stuff. If you want to test your ISO and not a burnt CD then read the downloading faq and learn to use one of the md5 checksum tools. An md5 file should have come does in the BitTorrent download (although BitTorrent is so reliable it's hardly needed), or can be downloaded from the mirrors. This will be better than the testcd check, and should be faster too.

By the way, testcd just does a bunch of md5 checks on parts of the ISO that are expected to be on the CD, but it can't do as complete of a check as checking the md5 sum of the entire ISO. And you avoid the extra overhead of trying to extract stuff from the ISO while running the tests.