Final answer:
The Supreme Court has allowed most penalties aside from death for adults under the Eighth Amendment while ruling that executing intellectually disabled individuals is unconstitutional, without establishing an explicit test for cruel and unusual punishment.
Step-by-step explanation:
In recent years, the Supreme Court has interpreted the Eighth Amendment's ban on cruel and unusual punishment to allow most penalties short of death for adults. Despite not establishing a definitive test for what constitutes such punishment, the Court has ruled on various methods of execution.
In the case of Bucklew v. Precythe, the Supreme Court permitted an execution method despite claims that it could cause undue suffering. Controversies persist, such as the composition of lethal injection drugs and their effects, and the debate on whether certain methods prolong suffering.
However, the Court also recognized a limit in the case of executing intellectually disabled individuals, ruling it unconstitutional. The Eighth Amendment's interpretation continues to evolve with societal norms and judicial rulings.