You could use lists() :
test::where('id' ,'>' ,0)->lists('id')->toArray();
NOTE : Better if you define your models in Studly Case format, e.g Test.
You could also use get() :
test::where('id' ,'>' ,0)->get('id');
UPDATE: (For versions >= 5.2)
The lists() method was deprecated in the new versions >= 5.2, now you could use pluck() method instead :
test::where('id' ,'>' ,0)->pluck('id')->toArray();
NOTE: If you need a string, for example in a blade, you can use function without the toArray() part, like:
test::where('id' ,'>' ,0)->pluck('id');