Trio to indicate act as part of test (5-5,4)
I believe the answer is:
three-point turn
'part of test' is the definition.
The definition suggests a singular noun which matches the answer.
'trio to indicate act' is the wordplay.
'trio' becomes 'three' (synonyms).
'to indicate' becomes 'point' ('point' can be a synonym of 'indicate').
'act' becomes 'turn' (theatre).
'three'+'point'+'turn'='THREE-POINT TURN'
'as' acts as a link.
Can you help me to learn more?
(Another definition for three-point turn that I've seen is " Driving manoeuvre".)