Unless I am missing something amidst all this talk of map and leaves (like the forest for the trees), there is no reason why you cannot simply specify the exact address of the data element that you want to retrieve.

map{$total_value+=$_->{test1}}@{$testsub->result()->[0]->{columns}}
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Off the top of my head this syntax may be wrong, gotta get on the other machine to check it.

Update: I did miss something, already answered.