Lung function tests are ordered to assess lung function, and whether disorders exist. Pulmonary function tests are commonly used to diagnose and follow up COPD, asthma, and pulmonary fibrosis. Pulmonary function tests are used preoperatively to assess and predict postop lung function if other surgical removal of a lobe were to be done. This test gives your doctor more detailed information about how well air moves in and out of your lungs. This is an integral part of the pulmonary assessment. Pulmonary function tests are performed by a licensed respiratory therapist.