A judicial warrant is a necessary component of the "normal need for law enforcement," because it protects privacy interests "by assuring citizens subject to a search or seizure that such intrusions are not the random or arbitrary acts of government agents. A warrant assures the citizen that the intrusion is authorized by law, and that it is narrowly limited in its objectives and scope. A warrant also provides the detached scrutiny of a neutral magistrate, and thus ensures an objective determination whether an intrusion is justified in any given case." (Skinner v. Railway Labor Executives' Assn, 489 U.S. at pp. 621-622 [109 S. Ct. at pp. 1415-1416]; see also Treasury Employees v. Von Raab, 489 U.S. at p. 666 [109 S. Ct. at p. 1391].) A warrant, however, provides little or no additional protection to personal privacy when, as in the present case, the circumstances justifying the testing and the permissible limits of the intrusion are defined narrowly and specifically, these circumstances doubtless are well-known to those in the class of persons to be tested, and the decision to test is not discretionary and thus is not based on a judgment that certain conditions are present. In such circumstances "there are simply 'no special facts for a neutral magistrate to evaluate,' " and it is reasonable to dispense with the warrant requirement. (Treasury Employees v. Von Raab, 489 U.S. at p. 667 [109 S. Ct. at p. 1391]; see also Skinner v. Railway Labor Executives' Assn, 489 U.S. at p. 622 [109 S. Ct. at p. 1416].)