What is the test for a finding that appellant waived his right to a jury trial on the basis that he admitted serving a prior prison term?

The parties agree the trial court erred in finding that appellant waived his right to a jury trial on the prior prison term allegation. ( 667.5, subd. (b).) However, appellant additionally contends the record does not demonstrate that he was advised of any of his constitutional rights pursuant to Boykin v. Alabama (1969) 395 U.S. 238 (Boykin), In re Tahl (1969) 1 Cal.3d 122 (Tahl), and In re Yurko (1974) 10 Cal.3d 857 (Yurko) or that he admitted serving a prior prison term. Appellant argues the court's error is reversible; the People argue the error is harmless.