Update tests for nbgrader assign
Update tests for nbgrader assign

jdfreder/nbgrader,modulexcite/nbgrader,EdwardJKim/nbgrader,jhamrick/nbgrader,ellisonbg/nbgrader,dementrock/nbgrader,jhamrick/nbgrader,alope107/nbgrader,jupyter/nbgrader,jupyter/nbgrader,EdwardJKim/nbgrader,MatKallada/nbgrader,dementrock/nbgrader,MatKallada/nbgrader,jdfreder/nbgrader,jhamrick/nbgrader,EdwardJKim/nbgrader,jupyter/nbgrader,alope107/nbgrader,modulexcite/nbgrader,ellisonbg/nbgrader,jupyter/nbgrader,EdwardJKim/nbgrader,jhamrick/nbgrader,ellisonbg/nbgrader,ellisonbg/nbgrader,jupyter/nbgrader