What is the legal test for proving a defendant has met their burden of proving that a cause of action has no merit?

"A defendant . . . has met his or her burden of showing that a cause of action has no merit if the party has shown . . . that there is a complete defense to the cause of action." ( 437c, subd. (p)(2).) "Once the defendant . . . has met that burden [by showing a complete defense to a cause of action], the burden shifts to the plaintiff . . . to show that a triable issue of one or more material facts exists as to [that] defense . . . ." (Ibid.; see Jessen v. Mentor Corp. (2008) 158 Cal.App.4th 1480, 1484-1485.) The plaintiff cannot rely upon a complaint's allegations "to show that a triable issue of material fact exists." ( 437c, subd. (p)(2).) Rather, the plaintiff must "set forth the specific facts showing that a triable issue of material fact exists as to [that] defense . . . ." (Ibid.)