What is the test for appointing a magistrate to hear a motion to dismiss?

Under 28 U.S.C. 636(b)(1)(A), a district court judge may designate a magistrate judge "...to hear and determine any pretrial matter pending before the court, except a motion...to dismiss for failure to state a claim upon which relief can be granted, and to involuntarily dismiss an action." Hunt v. Piller, 384 F.3d 1118, 1123 (9th Cir. 2004). However, the district court may "designate a magistrate to hear a motion to dismiss and submit proposed findings of fact and recommendations for the disposition of such a motion" under 28 U.S.C. 636(b)(1)(B). Id. at 1123. Within fourteen days, any party may serve and file written objections to a magistrate judge's findings in the report and recommendation. See 28 U.S.C. 636(b)(1). Once objections are made "[a] judge of the court shall make a de novo determination of those portions of the report...to which objection is made." Id. "A judge of the court may accept, reject, or modify, in whole or in part, the findings or recommendations made by the magistrate judge." Id.