It appears that the right-wing drug-enforcement legal/industrial lobby borrowed a page from the liberal side, by voting to "protect" the chronically sick from buying "tainted" marijuana from pot shops. They require that the pot being sold be tested for hazardous chemicals, such as pesticides, and for potency.
Of course, they knew that because of the precarious legal state of pot, that it would be very difficult to get labs into the business. Also, because of the difficulty in tracking a "lot" from a particular grower, the sampling used to test will always be suspect.
