The request would be made to the court during discovery and, if it was granted, the test would be done by an independent lab. The department could lose/destroy the evidence before it could be tested but that would likely prevent the evidence from being used at trail and it's hard to prosecute someone for a drug offence if you can't tell the jury that you found drugs. Ultimately it's not a great plan anyway. If they didn't find any finger prints then the prosecutor will find some "expert" to testify that drug dealers always wipe down their baggies and wear gloves, if they only find the officer's finger prints then he'll testify that he accidentally handled it without gloves while logging it into evidence.