def del_cert(self, student, course_id):

        """
        Arguments:
          student - User.object
          course_id - courseenrollment.course_id (string)

        Removes certificate for a student, will change
        the certificate status to 'deleting'.

        Certificate must be in the 'error' or 'downloadable' state
        otherwise it will return the current state

        """

        raise NotImplementedError