Part of artiste’s theatre trial (4)
I believe the answer is:
test
'trial' is the definition.
(I know that trial can be written as test)
'part of artiste's theatre' is the wordplay.
'part of' says the answer is hidden in the clue.
'TEST' is hidden in the letters of 'artistes theatre'.
(Other definitions for test that I've seen before include "big game" , "Sample" , "Trial; exam" , "water flowing through Hampshire" , "Evaluation" .)