What is the test for habeas corpus?

Habeas corpus was created in a time of change and one of its features is its ability to respond to changing environments. One of the points of the prerogative writ was its ability to create the means to have justice done even when the law had not previously provided those means. It was a creature of common law courts that was equitable in all but name. It was and is an instrument for the protection of vulnerable people. And while it was never narrow and formalistic it had, as “its grand purpose - the protection of individuals against the erosion of their rights to be free from wrongful constraints upon their liberty”. Jones v. Cunningham, 371 U.S. 236 (1962), at p. 243.