Initiation of this Italian test upset singer (6)
I believe the answer is:
tomtit
'singer' is the definition.
(tomtit is a songbird)
'initiation of this italian test upset' is the wordplay.
'initiation of' says to take the initial letters.
'italian' becomes 'it'.
'test' becomes 'mot'.
'upset' shows that the letters should be reversed in order.
The first letter of 'this' is 't'.
't'+'it'+'mot'='titmot'
'titmot' in reverse letter order is 'TOMTIT'.
(Other definitions for tomtit that I've seen before include "Popular name for a songbird" , "another bird gets both" , "Type of bird, may be blue" , "bird - with 25d" , "Small bird" .)