A 45 year old woman repos that she has been having increased involuntary loss of urine, which is especially pronounced when she is feeling nervous or while sitting at her desk. Jogging does not worsen the incontinence. She has not had these symptoms in the past and is otherwise healthy. She is not taking any medications and has never been pregnant. On physical examination, she is afebrile, with stable vital signs. Her abdomen is benign, and vaginal examination reveals no prolapse. Sensation in all extremities is intact, with good motor strength. Her gait is normal, and reflexes are intact. Her work-up reveals a negative urinalysis, and blood cultures and urine cultures are all negative. Serum glucose level and glycosylated hemoglobin level is normal. Which of the following tests would be the most appropriate next step in diagnosis?