What is the test used to determine whether a confession is voluntary?

involuntary confession. [Citation.]... [] 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.]... 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.]" (People v. Massie (1998) 19 Cal.4th 550, 576.)