As much as it sucks to call off a match at the last minute, Shirley the health conditions should dictate it, rather than the inconvenience it causes to the fans.
I mean, even if there are clear guidelines, e.g. if less than 5 positives the evening before the match goes on, what if there are an additional 10 positives the day of? Yes, the tests should be done first thing in the morning, but even that would not be enough advance notice for a number of fans.
So yeah, it's a clusterfuck, but what are the alternatives?