Yes, I would wear a mask, even outdoors, I don’t care who has or hasn’t been tested. These tests are not the most accurate and being in close quarters with a hundred people, none wearing masks or social distancing, during a pandemic is foolish IMO.
Remember, this virus doesn’t discriminate, if you are human you might catch it even if you are the President of the U.S. or the President of Notre Dame. You would think our leaders would now this by now (6 months in)?