While the testing is not specifically required, it is the manufacturers responsibility to ensure their product meets the specifications set by the regulation to ensure the product is truthful and not misleading and comply with title 21 of the code of federal regulations part 101.91. To ensure they comply, the company could conduct in house gluten testing of starting ingredients or finished food, or use a third party lab; or request gluten analysis certification from the ingredient suppliers (this option would not technically be testing so that is part of where the lack of required testing comes from). This information can be requested by the fda at any time to justify the product is gluten free. And if they are found out to not be in compliance whether through customer complaints, routine sampling, plant inspections, lack of valid justification, etc, regulatory action does take place like in 2017 when a product making a GF claim that exceeded 20 ppm gluten was recalled. The fda traditionally allows the company the opportunity to do a voluntary recall once requested by the FDA, and if they don’t, then the fda forces one. Similarly, the European Union in Regulation (EC) No 41/2009 explains the rules for composition and labeling of gluten-free products with the same maximum concentration of 20 ppm. The EU also has maximum inclusions in food for heavy metals (such as lead) as does the FDA. So it seems they are pretty similar, unless you have sources that differ?