What is the test for a sentence of life without parole for a convicted felon?

The Eighth Amendment prohibits the infliction of "cruel and unusual punishment." In arguing that his sentence violates the Eighth Amendment, appellant relies on Solem v. Helm (1983) 463 U.S. 277, 103 S.Ct. 3001, 77 L.Ed.2d 637. In Solem, a bare majority of the court held that a sentence of life without the possibility of parole was unconstitutionally disproportionate as applied to defendant on his seventh conviction of a nonviolent felony. The court stated,