What is the legal test to determine whether a state has a valid justification for its actions?

Assuming a contractual relationship has been substantially impaired, the next step is to examine the state's justification for its action. See Energy Reserves, 459 U.S. at 411, 103 S.Ct. at 704. The law must have a "legitimate public purpose." Id. It should be aimed at remedying an important "general social or economic problem" rather than "providing a benefit to special interests." Id. at 412, 103 S.Ct. at 705. Sometimes this inquiry must be approached on a provision-by-provision basis--statutes aimed at solving broad societal problems may contain language whose only purpose is to benefit a small interest group. See, e.g., Garris v. Hanover Ins. Co., 630 F.2d 1001, 1009-10 (4th Cir.1980) (statute as a whole had broad general purpose, but challenged provision aimed at benefiting small interest group).