The very question, “How did God test the angels?” assumes that God DID test the angels upon no evidence at all. Reminds one of the Talmudic scholars trying to decide how large the skirt of a Jew must be to allow the men to take hold of it.
Talmudic scholars and Catholic (and Orthodox) Christians share one thing in common: we understand that Revelation transcends the Written Word but that the key to understanding and explaining the Written Word was transmitted orally through various vehicles. We Christians differ with Talmudic scholars as to the source, contents, and purpose of this "key".
In other words, I'm not beholden to sola scriptura. Holy Scripture, as holy and valuable (and Sacrmental!) as it is, is not the sole rule of faith and morals for Christians. Not even Scripture attests to that. Nor do I think that Holy Scripture is a collection of propositional truths - although it does contain a number of propositional truths - to which theological research must be beholden to. Such a restriction was the Reformers' invention and I reject their rubric.
However, I respect your choice of abiding by their judgment. I'm not interested in getting into an extended discussion on the demerits of sola scriptura for others have done a better job at that than I.
I understand that a strict adhesion to sola scriptura will keep you away from a deeper Catholic exegesis of the Word because it chunks the Word of its interpretative key as known and handed down by the Apostles, Fathers, and Doctors of the Church. I'll have to leave it at that.
+JMJ,
-Theo