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题目来源：


廖雪峰python教程


原题目代码：

import unittest

class Student(object):
    def __init__(self, name, score):
        self.name = name
        self.score = score
    def get_grade(self):
        if self.score >= 60:
            return 'B'
        if self.score >= 80:
            return 'A'
        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()

运行结果：



可以看到测试有2处错误，第一处在line 19处，使用get_grade方法时断言错误。回头查看，发现get_grade方法定义时不准确，应该先判断≥80，再判断≥60.第二处错误在line 38，使用get_grade方法输入的grade没有限制范围。回头添加限制条件，使 0≥grade≥100时，方法正确调用，否则raise 一个 ValueError

修改后的代码如下：

import unittest

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