What is the test for obtaining a search warrant from a witness who has witnessed a crime?

upon their information, should be considered reliable. . . . [N]either a previous demonstration of reliability nor subsequent corroboration is ordinarily necessary when witnesses to or victims of criminal activities report their observations in detail to the authorities." (Id. at p. 269, fn. omitted; see also Soli v. Superior Court (1980) 103 Cal.App.3d 72, 82-83 (Soli) ["information from one reasonably believed to be the victim of a reported crime will be deemed reliable, thus furnishing Fourth Amendment probable cause for a search warrant"].)