Add test to check that extra notebooks are skipped
Add test to check that extra notebooks are skipped

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