What is the test for whether a defendant is voluntarily absent from a trial?

In determining whether a defendant is voluntarily absent, the touchstone of the analysis is whether the defendant's absence was intended to thwart the pending proceedings. (Lewis, supra, 144 Cal.App.3d at p. 276 ["The defendant's constitutional right to be present at his trial can be surrendered ... if it is abused for the purpose of frustrating the trial."]; Gutierrez, supra, 29 Cal.4th at pp. 1204-1205 [restrictions on the defendant's right to be present at his trial were "'designed to prevent the defendant from intentionally frustrating the orderly processes of his trial by voluntarily absenting himself'"]; People v. Pigage (2003) 112 Cal.App.4th 1359, 1369 (Pigage) ["'A crucial question must always be, "Why is the defendant absent?"'"]; United States v. Partlow (1970) 428 F.2d 814, 816 (Partlow) ["we cannot presume the waiver of constitutional rights"].)