What is the legal test for a search warrant under section 871.5 of the Penal Code?

"On review under [Penal Code] section 871.5, the superior court is bound by the magistrate's findings if they are supported by substantial evidence. But it is the duty of the superior court, and ours as well, to measure those facts, as found by the magistrate, against the constitutional standard of reasonableness. The constitutional issue is solely a question of law and if the magistrate mistakenly concluded that a search was unconstitutional that conclusion is also erroneous 'as a matter of law.' " (People v. Salzman (1982) 131 Cal.App.3d 676, 684, 182 Cal.Rptr. 748.)