Since i have had trouble with my breathing. how do they test for asthma?

Testing: A lot of different medical problems have similar symptoms to asthma. The best way to confirm the diagnosis is with a methacholine challenge test - a special type of pulmonary function test. Your breathing is tested while a therapist gives you an inhaled medication called methacholine. In patients with asthma, this will cause the airways to spasm at low doses - a "positive" test.