What is the test for determining the validity of an administrative ruling?

"... '[I]n determining the proper interpretation of a statute and the validity of an administrative regulation, the administrative agency's construction is entitled to great weight, and if there appears to be a reasonable basis for it, a court will not substitute its judgment for that of the administrative body.' [Citations.] In addition, an administrative ruling ' "comes before the court with a presumption of correctness and regularity, which places the burden of demonstrating invalidity upon the assailant [fn. omitted]." [Citations.]' " (Campbell Industries v. Board of Equalization (1985) 167 Cal.App.3d 863, 868, 213 Cal.Rptr. 533.)