What is the test for probable cause in a personal injury action?

5 Although separately stated, probable cause and prior favorable termination are just two elements of the same prerequisite. The requirement of a favorable termination of the prior action is used as a threshold indicator of the lack of probable cause, without which the courts will not even consider the issue. "[T]he rule tends to eliminate unnecessary litigation," because a judgment adverse to the defendant in the prior action "operates to establish conclusively that the plaintiff had probable cause." (Babb v. Superior Court, supra, 3 Cal.3d at p. 847, 92 Cal.Rptr. 179, 479 P.2d 379.)