Acid or screen follower (4)
I believe the answer is:
test
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">acid or screen follower</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for test that I've seen before include "Trial; Hampshire river" , "Short exam" , "Trial; cricket match" , "Trial - international game" , "Critical examination or trial of qualities or abilities" .)