Cross being put in same complex tests (5)
I believe the answer is:
exams
'tests' is the definition.
('exam' can be a synonym of 'test')
'cross being put in same complex' is the wordplay.
'cross' becomes 'x' (X is cross-shaped).
'being put in' means one lot of letters goes inside another.
'complex' is an anagram indicator.
'same' anagrammed gives 'eams'.
'x' inserted within 'eams' is 'EXAMS'.
(Other definitions for exams that I've seen before include "Set of exercises evaluating knowledge (abbr)" , "GCSE, A-level, etc" , "Tests, in short" , "finals?" , "Important tests" .)