What is the test for confrontation in a witness case?

"Although important, the constitutional right of confrontation is not absolute. [Citations.] 'Traditionally, there has been "an exception to the confrontation requirement where a witness is unavailable and has given testimony at previous judicial proceedings against the same defendant [and] which was subject to cross-examination." ' " (People v. Herrera (2010) 49 Cal.4th 613, 621.) "A witness who is absent from a trial is not 'unavailable' in the constitutional sense unless the prosecution has made a 'good faith effort' to obtain the witness's presence at the trial." (Id. at p. 622.) We apply the de novo standard of review. (People v. Friend (2009) 47 Cal.4th 1, 68.)