What is the test for consent of a defendant in a criminal case?

'In Hopt v. Utah, 110 U.S. 574, 579 (4 Sup.Ct. 202, 28 L.Ed. 262), this court, observing that the public has an interest in the life and liberty of an accused person, said: 'Neither can be lawfully taken except in the mode prescribed by law. That which the law makes essential in proceedings involving the deprivation of life or liberty cannot be dispensed with or affected by the consent of the accused, much less by his mere failure, when on trial and in custody, to object to unauthorized methods."

And then Justice Harlan added:

'The present defendant may be guilty, and may deserve the full punishment imposed upon him by the sentence of the trial court. But it were better that he should escape altogether than that the court should sustain a judgment of conviction of an infamous crime where the record does not clearly show that there was a valid trial.'

In Low v. United States, 169 F. 86, 94 C.C.A. 1 (1909), Mr. Justice Lurton said: