Thoracic outlet syndrome

An 18-year-old female comes to the clinic complaining of weakness and loss of sensation in her left arm and hand as if she had "hit her funny bone." She reports that this weakness and loss of sensation started after she had a car accident a couple of weeks ago during which she dislocated her shoulder. Her shoulder "popped right back in" so she did not receive medical attention at the time. Physical examination shows mild edema in her arm and that her strength is only a 4/5 on the left while it is 5/5 on the right. Which test(s) could be used to confirm your diagnosis?