Test offered by sequence in exposed cards? (5,3)
I believe the answer is:
dummy run
'test' is the definition.
(a dummy run is a practice or test)
'by sequence in exposed cards?' is the wordplay.
'by' is a charade indicator (letters next to each other).
'sequence' becomes 'run' (I've seen this in another clue).
'in exposed cards?' becomes 'dummy' (I can't justify this - if you can you should believe this answer much more).
'run' put after 'dummy' is 'DUMMY RUN'.
'offered' is the link.
(Other definitions for dummy run that I've seen before include "Practice, trial" , "A try-out or test" , "Rehearsal" , "Practice session" .)