An excellent way to test one’s understanding of QGD is to read critically articles that provide sound arguments against its proposition. A good recent example if an article by Brian Koberlein titled Dying Light.
In his article, Koberlein provides sound arguments again photons having mass. Since QGD axiom set implies that photons have mass, such article provides a good test of one’s understanding of QGD it’s counter arguments.
Below is my Koberlein’s article annotated by me. I outlined the main arguments in the article and provided counterarguments.