What is the test for establishing that a defendant has not been subjected to custodial interrogation?

"When reviewing a trial court's determination that a defendant did not undergo custodial interrogation, an appellate court must 'apply a deferential substantial evidence standard' [citation] to the trial court's factual findings regarding the circumstances surrounding the interrogation, and it must independently decide whether, given those circumstances, 'a reasonable person in [the] defendant's position would have felt free to end the questioning and leave.'" (People v. Leonard (2007) 40 Cal.4th 1370, 1400.) Applying those standards, we conclude the trial court correctly determined that a reasonable person in Paz's position would not believe he was under arrest during his interrogation.