Regarding Covid testing results - if you want to get geeky this is a very good article that explains some of the complications of test result analysis. It's well written.
Bayes’ Rule, Decision Making, And Containing COVID-19 With Unreliable Diagnostic Tests
How false-negatives in diagnostic testing leads to release of infected people, and why extreme containment measures have been implemented.towardsdatascience.com
That article looks pretty good on the general complications and possible inaccuracies of testing
But a lot of the detail is a very tough read, so much of the graphs and algebra were beyond this mere humanities type's grasp
I hope some of the more specialist-minded on here grasp it better!