Who would be testing something like that, before using them?
The buyer/wholesaler. Its a facemask not the Space Shuttle, if you bought a supply of N95 facemarks would you not ensure they are N95 spec? Im not a Purchasing Officer but surely this is Purchasing Officer 101? Its China so check more, its Covid-19 so be sure.
The correct scenario is they arrived, and were found non compliant to N95 spec so sent back for a credit. Not sued an age later, which makes it seem a political issue.
Were they faulty, fake or just unsuitable? You can get N95/FPP2 masks with valves that may work fine as far as breathing in but don't stop the wearer spreading outgoing air. You would have to know more than just grab any N95 masks on offer.