What is the "necessity" test for determining whether a restriction or restriction on a prisoner's constitutional rights is restrictive enough to be struck down?

The lead case adopting the "necessity" test is Teterud v. Burns, supra, 522 F.2d 357. Teterud requires courts to be "as vigilant in protecting a prisoner's constitutional rights as we are in protecting the constitutional rights of a person not confined." (Id., at p. 359.) Accordingly, "a regulation which is more restrictive than necessary to meet ... institutional objectives or which does not serve the objectives advanced will be struck down." (Ibid.)