In fact, In re Kemmler, 136 U.S. 436 (1890) considered a constitutional challenge to the electric chair and rejected it on the merits. The merits, at that time, meant that it did not violate the Due Process Clause or the Privileges and Immunities Clause, as the Eighth Amendment had not then been “incorporated.”

In Gomez v. U.S. District Court, 503 U.S. 653 (1992), also involved a constitutional challenge, this time to the gas chamber. Although the majority decided to vacate the stay on procedural grounds, I would still say that the court “faced a constitutional test,” although I suppose one could quibble about what “faced” means.

In dissent, Justice Stevens noted that the gas chamber was unnecessary because of the superiority of lethal injection, a conclusion “of numerous medical, legal, and ethical experts.” Id., at 656.

[Various dissents from cert. suggested various justices wanted to ... Stevens in one opinion suggested lethal injection was the only legitimate means of execution]

Of course, lethal injection has not been a core means of execution for the last hundred years … only for a few decades. And, other matters were focused upon as well.

Anyway, the issue here is the means of lethal injection, and there is some good evidence that the “protocol” was set up in a shoddy way, and that a better one is possible given the quoted test.