Is testing pants getting most tight (9)
I believe the answer is:
stingiest
'most tight' is the definition.
('stingy' can be similar in meaning to 'tight')
'is testing pants' is the wordplay.
'pants' indicates an anagram (UK informal term for 'nonsense' or 'rubbish').
'is'+'testing'='istesting'
'istesting' is an anagram of 'STINGIEST'.
'getting' acts as a link.
(Other definitions for stingiest that I've seen before include "The worst nettles" , "may be very near" .)