class Student(object):

def __init__(self, name, score):
    self.name = name
    self.score = score
def get_grade(self):
    if self.score >= 60 and self.score < 80:
        return 'B'
    elif self.score >= 80 and self.score <= 100:
        return 'A'
    elif self.score <0 or self.score > 100:
        raise ValueError
    return 'C'

class TestStudent(unittest.TestCase):

def test_80_to_100(self):
    s1 = Student('Bart', 80)
    s2 = Student('Lisa', 100)
    self.assertEqual(s1.get_grade(), 'A')
    self.assertEqual(s2.get_grade(), 'A')

def test_60_to_80(self):
    s1 = Student('Bart', 60)
    s2 = Student('Lisa', 79)
    self.assertEqual(s1.get_grade(), 'B')
    self.assertEqual(s2.get_grade(), 'B')

def test_0_to_60(self):
    s1 = Student('Bart', 0)
    s2 = Student('Lisa', 59)
    self.assertEqual(s1.get_grade(), 'C')
    self.assertEqual(s2.get_grade(), 'C')

def test_invalid(self):
    s1 = Student('Bart', -1)
    s2 = Student('Lisa', 101)
    with self.assertRaises(ValueError):
        s1.get_grade()
    with self.assertRaises(ValueError):
        s2.get_grade()

if name == 'main': unittest.main()