Cook beans in a large pot of boiling salted water until tender, 5 minutes.
Remove with a slotted spoon.
Cool completely, by plunging into cold water, and reserve.
Add potatoes to the pot and cook until tender in the centre when pierced with the tip of a small, sharp knife, 6-8 minutes.
Remove with a slotted spoon and reserve.
Add pasta to the pot and cook until firm to the bite if serving hot or just firm to the bite if serving as a salad.
Return beans and potatoes to pot just before draining pasta, to heat through, 1 minute.
Drain pasta, beans and potatoes, reserving 1/2 cup water.
Return pasta, beans and potatoes with the pesto and olive oil to the warm pasta pot.
Toss well, adding reserved water as needed.
Add salt to taste.
Serve immediately or at room temperature.