A trial to net billions, if everything goes perfectly (2,4)
I believe the answer is:
at best
'everything goes perfectly' is the definition.
I can't judge whether this definition defines the answer.
'a trial to net billions' is the wordplay.
'trial' becomes 'test' (synonyms).
'to net' means one lot of letters goes inside another.
'billions' becomes 'b' (abbreviation).
'test' placed around 'b' is 'tbest'.
'a'+'tbest'='AT BEST'
'if' acts as a link.
Can you help me to learn more?
(Other definitions for at best that I've seen before include "In the most optimistic scenario" , "In the optimal situation" , "In the most favourable outcome" , "Taking the most hopeful view" , "In the most favourable circumstances" .)