What is the test for admissibility of a confession in a criminal case?

1 Evidence Code section 402 provides: "(a) When the existence of a preliminary fact is disputed, its existence or non-existence shall be determined as provided in this article. [p] (b) The court may hear and determine the question of the admissibility of evidence out of the presence or hearing of the jury; but in a criminal action, the court shall hear and determine the question of the admissibility of a confession or admission of the defendant out of the presence and hearing of the jury if any party so requests. [p] (c) A ruling on the admissibility of evidence implies whatever finding of fact is prerequisite thereto; a separate or formal finding is unnecessary unless required by statute."

2 Miranda v. Arizona (1966) 384 U.S. 436, 86 S.Ct. 1602, 16 L.Ed.2d 694.