You can send any unsealed product to a lab for chromatography, or you can get bloodwork done to see if your testosterone is beyond endogenous levels. How long you wait to get bloods in the scenario you suspect you have fake product depends on the ester you are using. For a long ester like enanthate, I'd probably wait 4 weeks or more before bothering to get bloodwork to see if it's bunk. Under normal circumstances I would normally wait about 6 weeks to draw blood for enanthate though, since it is slow to build up even when it is real.