What is the test for proving a due process violation?

"One of the basic tenets of the California [Administrative Procedure Act] ... is that, to promote both the appearance of fairness and the absence of even a probability of outside influence on administrative hearings, the prosecutory and, to a lesser extent, investigatory, aspects of administrative matters must be adequately separated from the adjudicatory function." ( Nightlife Partners v. City of Beverly Hills (2003) 108 Cal.App.4th 81, 91, 133 Cal.Rptr.2d 234, italics omitted.) "To prove a due process violation

[62 Cal.App.5th 23]