What is the test for finding that a pat-down search conducted by an off-duty police officer was consensual?

We conclude that the district court did not clearly err in finding, based on the totality of the circumstances, that "the three-minute interview with defendant--from the Officer's initial approach until defendant's arrest, including the pat-down search, was a consensual encounter" and that appellant voluntarily consented to the pat-down search of his person. Because we conclude that the encounter was consensual, and not an investigative detention, we need not consider whether it was otherwise supported by articulable, reasonable suspicion that appellant had committed or was about to commit a crime. See, e.g., United States v. Low, 887 F.2d 232, 235 (9th Cir.1989).