Not yet proven (8)
I believe the answer is:
untested
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not yet proven</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for untested that I've seen before include "Not yet proven" , "Not tried or put to proof" , "New" , "learner driver" , "Pilot may be" .)