DALLAS — Subway Restaurants will begin testing a gluten-free roll and a gluten-free brownie starting the week of Jan. 10 in the markets of Dallas-Fort Worth and Tyler, Tex., according to the web site www.celiac.com. The rolls and brownies will be prepackaged and individually wrapped. A tutorial video will instruct restaurant employees on how to cut the roll with a pre-wrapped knife that is used only once. The same employee will prepare a gluten-free order from beginning to end, which means only one set of hands will touch the sandwich.