What is the test for a warrant under the Fourth Amendment?

"The essential protection of the warrant requirement of the Fourth Amendment" relies upon "a neutral and detached magistrate." (Illinois v. Gates, supra, 462 U.S. at p. 240, 103 S.Ct. at p. 2333.) The magistrate acts as a trier of fact in appraising and weighing the affidavit. (People v. Stout (1967) 66 Cal.2d 184, 193, 57 Cal.Rptr. 152, 424 P.2d 704.) He may reject an affidavit as not credible or not sufficient. He may also "before issuing the warrant, examine on oath the person seeking the warrant and any witnesses he may produce...." (Pen.Code, 1526.)