What is the test for making a criminal threat against a classmate?

The juvenile court found true the allegation that then-13-year-old T.J. made a criminal threat (Pen. Code, 422)¹ by placing a "hit list" in his middle school classmate's backpack. On appeal, T.J. challenges the sufficiency of the evidence supporting the true finding, contending the victim did not suffer "sustained fear" as required by section 422. T.J. further contends the juvenile court erred by admitting statements he made to police because he was subjected to custodial interrogation without first being advised of his rights under Miranda v. Arizona (1966) 384 U.S. 436 (Miranda). We affirm.