Correct me if I'm wrong, but I don't think that the test kits that are now (Marquis, etc) can tell you whether methylone/ mephedrone are present.. I'm no chem expert, but I'm gonna assume that the chemical makeup is different enough to affect this?
We have a test kit that's starting to go bad, but when I tested some "white powders" that we got, it didn't react at all. Consuming these mystery powders didn't really interest me, so I didn't, but I suspect that it was methylone or mephedrone.