Some badger's lair taken up for tests (6)
I believe the answer is:
trials
'for tests' is the definition.
('trial' can be a synonym of 'test')
'some badger's lair taken up' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'up' is a reversal indicator (in down clue: letters go upwards).
'slairt' is hidden in the letters of 'badgers lair taken'.
'slairt' written backwards gives 'TRIALS'.
(Other definitions for trials that I've seen before include "Attempts" , "Tribulations" , "Court hearings or experiments" , "Legal proceedings or tests of endurance" , "Court cases or ordeals" .)