I swear I heard testimony regarding GZ being tested for alcohol/drugs, but you seem pretty certain. Did the police testify to GZ being sober? I know this issue was discussed in court.
For what it’s worth... a Google search of “Zimmerman drug test” calls up a bunch of cites, some reliable, that seem to indicate that St. Trayvon was tested but Zimmerman was not.
Not proof, just evidence — put whatever weight on it you want.