What is the test for determining whether a prison regulation impinges on inmates' constitutional rights?

"[W]hen a prison regulation impinges on inmates' constitutional rights, the regulation is valid if it is reasonably related to legitimate penological interests." Turner v. Safely, 482 U.S. 78, 89 (1987). If, however, the inmate can demonstrate alternatives to the regulation that accommodate the inmate's constitutional rights with minimal effect on valid penological interests, a court may consider such alternatives as evidence that the regulation does not satisfy the reasonable relationship standard. Id. at 90.