What is the test for terminating the natural parent's right to adopt a child?

There should be no doubt about the applicable federal constitutional principle. The state may not sever completely and irrevocably the rights of parents in their natural child unless the justification for such action is proved by the state by at least clear and convincing evidence. (Santosky v. Kramer, supra, 455 U.S. at p. 747-748, 102 S.Ct. at p. 1391.) Moreover, it seems evident that this justification, however it may be articulated by a particular state statute, cannot be based solely upon a consideration of the best interests of the child. (Santosky, at p. 760, fn. 10, 102 S.Ct. at p. 1398, fn. 10; see also Adoption of Kelsey S. (1992) 1 Cal.4th 816, 849-851, 4 Cal.Rptr.2d 615, 823 P.2d 1216.) Instead, termination must rest upon a judicial adjudication that the parents are "unfit to raise their own children." ⁵ (Santosky, 455 U.S. 745, 760, 102 S.Ct. 1388, 1398.) Until such a determination is made, the child and his or her parents are not adversaries, and "share a vital interest in preventing erroneous termination of their natural relationship." (Id., at p. 760, 102 S.Ct. at p. 1398.) Thus, the constitutional measure of clear and convincing evidence must be employed at the point in the proceeding when the critical factual determination of parental unfitness is made. (Id. at pp. 768-769, 102 S.Ct. at pp. 1402-1403.)