What is the test for accepting a guilty plea in a criminal case?

In Boykin v. Alabama (1969) 395 U.S. 238 (Boykin), the high court held it was error to accept a guilty plea "without an affirmative showing that it was intelligent and voluntary." (Id. at p. 242.) The court explained: "Several federal constitutional rights are involved in a waiver that takes place when a plea of guilty is entered in a state criminal trial. First, is the privilege against compulsory self-incrimination . . . . [Citation.] Second, is the right to trial by jury. [Citation.] Third, is the right to confront one's accusers." (Id. at p. 243.) The court held that "[w]e cannot presume a waiver of these three important federal rights from a silent record." (Ibid.)