What is the test for consent to search for methamphetamine?

Once officers were in defendant's residence, they observed numerous televisions, VCRs, microwave ovens, tools and other items stacked in the living room. Believing the items to be stolen, officers confronted defendant with their suspicion and asked if he would consent to a search of the premises. Defendant assured officers there was no stolen property on the premises and signed a written form authorizing them to search the residence. During the ensuing search, officers found 68 grams of methamphetamine inside a metal box. After waiving his Miranda rights (Miranda v. Arizona (1966) 384 U.S. 436, 86 S.Ct. 1602, 16 L.Ed.2d 694), defendant showed officers "other items of narcotics."