My son had a record of childhood asthma, received a pro forma DQ and had to take the test. It is intended to stress your lungs, so it will not be fun, but don't worry about it, including how to ace it or how well you are doing while it is going on. Based on your description of your conditioning, you should be able to get a waiver.
We had to go through the Methacholine Challenge Test. It's actually a test of your Bronchial tubes intending to bring about an adverse/asthmatic episode. There is nothing you can do to prepare for it. During the test his/her bronchial tubes will eventually constrict. It's just a matter of when and at what level. The test is a series of loops with the Methacholine (a histamine) administered in increasing amounts through a nebulizer. They'll start with baseline tests with simple saline to establish the baseline. Then increase the methacholine with each additional loop with a total of 6-7 total loops. Once they finish they'll give him/her an antihistamine to return the bronchial tubes back to normal. The test will take 60-90 minutes. It's not much fun. One of the issues is finding a pulmonary lab that has the ability to run & administer the test.