Practice or trial (5,3)
I believe the answer is:
dummy run
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">practice</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">trial</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for dummy run that I've seen before include "Practice session" , "A try-out or test" , "Practice, trial" , "Rehearsal" .)