If it's enough to test then it's enough to charge. They'll scrape everything in the back together just to get enough.
If a criminalist determines that the residue is a useable amount, then the state can charge use with posession. You should contact a qualified attorney to discuss any potential issues to pursue with your case.
Yes. The true question will be whether or not you knew, or had reason to know, that the bag had a meth residue in it.
As my colleagues mentioned, in Arizona, it is illegal to be in possession of an illegal substance when you either knew or had reason to know that the substance was illegal. If there is enough residue in the container to test, the prosecutor will be able to move forward with charges. It is critical that you contact a lawyer who is experienced with possession of drug paraphernalia cases.
Matthew L. Lopez, Esq.
Matthew Lopez Law, PLLC
7551 S. Willow Dr., Ste. 102
Tempe, AZ 85283