'Asserts whether the given course_grade is as expected with
zero values.'

def _assert_zero_grade(self, course_grade, expected_grade_class):

    self.assertIsInstance(course_grade, expected_grade_class)
    self.assertIsNone(course_grade.letter_grade)
    self.assertEqual(course_grade.percent, 0.0)
    self.assertIsNotNone(course_grade.chapter_grades)
