sausage white bean and tortellini soup

Ingredients

• 1 tablespoon olive oil
• 4 ounces hot sausages, removed from casings
• 1 onion, chopped
• 1 medium rib celery, chopped (about 2/3 cup)
• One 15-ounce can white beans, such as cannellini or navy, rinsed and drained
• One 15-ounce can diced tomatoes
• 2 cups low-sodium chicken broth
• One 8- to 9-ounce package of your favorite refrigerated tortellini
• Salt and freshly ground black pepper
• 1/4 cup prepared pesto