Testing hearing (6)
I believe the answer is:
trying
I believe this is a double definition.
'testing' is the first definition.
('try' can be a synonym of 'test')
'hearing' is the second definition.
('try' can be a synonym of 'hear')
(Other definitions for trying that I've seen before include "Stressful" , "Making attempts" , "Tiresome" , "responsibility of the first Baron Jeffreys of Wem" , "Exasperating" .)