What is the test for admitting unsubstantiated or unreliable evidence as substantive evidence in a probation revocation proceeding?

"Despite the relaxed rules of evidence governing probation revocation proceedings, a court is not permitted ' "to admit unsubstantiated or unreliable evidence as substantive evidence ...." ' [Citation.] [] As long as hearsay testimony bears a substantial degree of trustworthiness it may legitimately be used at a probation revocation proceeding. [Citations.] In general, the court will find hearsay evidence trustworthy when there are sufficient 'indicia of reliability.' [Citation.] Such a determination rests within the discretion of the trial court and will not be disturbed on appeal absent an abuse of discretion." (People v. Brown (1989) 215 Cal.App.3d 452, 454-455.)³