What is the test for calling a witness an accomplice?

"'If there is evidence from which the jury could find that a witness is an accomplice to the crime charged, the court must instruct the jury on accomplice testimony. [Citation.] But if the evidence is insufficient as a matter of law to support a finding that a witness is an accomplice, the trial court may make that determination and, in that situation, need not instruct the jury on accomplice testimony.' [Citation.]" (People v. Gonzales (2011) 52 Cal.4th 254, 302 (Gonzales).)