Trial a combination of having no booze and exercise (3,3)
I believe the answer is:
dry run
'trial' is the definition.
(I've seen this before)
'having no booze and exercise' is the wordplay.
'having no booze' becomes 'dry' (dry can mean abstaining from drinking alcohol).
'and' is a charade indicator (letters next to each other).
'exercise' becomes 'run' (running is a type of exercise).
'dry'+'run'='DRY RUN'
'a combination of' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for dry run that I've seen before include "Practice session in preparation for public performance" , "event staged by AA?" , "A dummy test - sounds thirsty" , "Thirsty sort of rehearsal?" , "Kind of rehearsal like thirsty trot" .)