What is the legal test for indemnity for a non-tortfeasor in a medical malpractice action?

Obviously, in most cases the jury will not award plaintiff all of the damages sought and will not conclude the settling tortfeasor should have borne the lion's share. But because prior to trial these matters are necessarily uncertain and the possibility of establishing bad faith exists, the nonsettling tortfeasor's counsel must continue to maintain his cross-complaint for total and partial indemnity. (Cf. Smith v. Lewis (1975) 13 Cal.3d 349, 360, 118 Cal.Rptr. 621, 530 P.2d 587 (failure to pursue arguable claims may constitute malpractice).) Aware that his settlement will not ordinarily prevent his participating in the litigation of the issues of damages and relative fault and that he might be held liable for further damages, a defendant contemplating settlement will rarely do so alone.