What is the test for a jury trial in a criminal case?

"The guarantees of jury trial in the Federal and State Constitutions reflect a profound judgment about the way in which law should be enforced and justice administered. A right to jury trial is granted to criminal defendants in order to prevent oppression by the Government.... Providing an accused with the right to be tried by a jury of his peers gave him an inestimable safeguard against the corrupt or overzealous prosecutor and against the complaint, biased, or eccentric judge." (emphasis added) Duncan v. Louisiana, 391 U.S. 145, 155-156, 88 S.Ct. 1444, 1450-1451, 20 L.Ed.2d 491.