A 10-year-old boy presents with a history recurrent abdominal pain. There is a past history of bronchitis but no history of pneumonia. On examination, there has been no significant increase in weight over the past 3 years, with flattening of the growth curve. Trace digital clubbing is noted. Most appropriate test to be ordered at this time is?
Pulmonary function tests Sweat test Chest x-ray Abdominal x-ray