What is the test for a federal court to review a motion for writ of habeas corpus brought by a person in custody pursuant to a state court judgment?

A district court "may accept, reject, or modify, in whole or in part, the findings or recommendations made by the magistrate." 28 U.S.C. 636(b)(1). If a party objects to any portion of the report, the district court "shall make a de novo determination of those portions of the report . . . to which objection is made." Id. A federal court may review a petition for writ of habeas corpus by a person in custody pursuant to a state court judgment "only on the ground that he is in custody in violation of the Constitution or laws or treaties of the United States." 28 U.S.C. 2254(a); accord Williams v. Taylor, 529 U.S. 362, 375 n.7 (2000).