What is the test for determining whether a confession is voluntary?

"Under the due process clauses of both the Fourteenth Amendment to the United States Constitution and article I, sections 7 and 15, of the California Constitution, these principles are established: an involuntary confession or admission is inadmissible; a statement is involuntary if it is the product of coercion or, more generally, 'overreaching'; involuntariness requires coercive activity on the part of the state or its agents; and such activity must be, as it were, the 'proximate cause' of the statement in question, and not merely a cause in fact. [Citation.]" (People v. Mickey (1991) 54 Cal.3d 612, 647.)

"Under both state and federal law, courts apply a 'totality of circumstances' test to determine the voluntariness of a confession. [Citations.] Among the factors to be considered are ' "the crucial element of police coercion [citation]; the length of the interrogation [citation]; its location [citation]; its continuity" as well as "the defendant's maturity [citation]; education [citation]; physical condition [citation]; and mental health." ' [Citation.]" (People v. Massie (1998) 19 Cal.4th 550, 576.) "In determining whether a confession was voluntary, '[t]he question is whether defendant's choice to confess was not "essentially free" because his will was overborne.' [Citation.]" (Ibid.) "Whether the defendant lost his free will and made involuntary statements does not rest on any one fact, however significant it may seem." (People v. DePriest, supra, 42 Cal.4th at pp. 34-35.)