Tests former ace missing shots initially (5)
I believe the answer is:
exams
'tests' is the definition.
('exam' can be a synonym of 'test')
'former ace missing shots initially' is the wordplay.
'former' becomes 'ex'.
'initially' suggests taking the first letters.
The initial letters of 'ace missing shots' is 'ams'.
'ex'+'ams'='EXAMS'
(Other definitions for exams that I've seen before include "School tests" , "Knowledge tests" , "Student assessments" , "papers" , "Important tests" .)