What is the legal test for appointing a guardian ad litem in a civil case?

"The guardian Ad litem and her attorneys were without power to enter into and the court was without power to approve the stipulation. Section 196a of the Civil Code provides that a civil suit in behalf of a minor illegitimate child to enforce the obligation of a parent to support it may be maintained by a guardian Ad litem and in such action the court has power to order and enforce the performance of such obligation. The [100 Cal.App.3d 544] power of a guardian Ad litem in such an action is not unlimited. In effect the court is the guardian, and the person named as guardian Ad litem is an officer of the court appointing him and is the agent of the court." (Berry v. Chaplin, supra, 74 Cal.App.2d 652, 657, 169 P.2d 442, 446-447.) In the sentence immediately following the passage cited by petitioner, the court stated, "It is the duty of a guardian Ad litem to protect or defend a suit, as the case may be." (Id., at p. 658, 169 P.2d at p. 447.) Literally the guardian ad litem is one "appointed for the purposes of the suit." (Black's Law Dict. (4th ed. 1951) p. 57, col. 1.)