Liar not upset when being tested (2,5)
I believe the answer is:
on trial
'being tested' is the definition.
(I've seen this before)
'liar not upset' is the wordplay.
'upset' indicates anagramming the letters.
'liar'+'not'='liarnot'
'liarnot' with letters rearranged gives 'ON TRIAL'.
'when' is the link.
(Other definitions for on trial that I've seen before include "In court to answer charges" , "Undergo court proceedings - being tested" , "heard?" , "Undergoing court process" , "Facing action" .)