In a large bowl, mix the 3 different types of beans, the celery, onion (drained), parsley and rosemary.

In a separate small bowl, whisk together the vinegar, sugar, olive oil, salt and pepper. Add the dressing to the beans. Toss to coat.

Chill beans in the refrigerator for several hours, to allow the beans to soak up the flavour of the dressing.