python unittest assertRaises

Question

我从 python.org unittest 文档中逐字复制了这个：

import random
import unittest

class TestSequenceFunctions(unittest.TestCase):

    def setUp(self):
        self.seq = range(10)

    def test_shuffle(self):
        # make sure the shuffled sequence does not lose any elements
        random.shuffle(self.seq)
        self.seq.sort()
        self.assertEqual(self.seq, range(10))

        # should raise an exception for an immutable sequence
        self.assertRaises(TypeError, random.shuffle, (1,2,3))

    def test_choice(self):
        element = random.choice(self.seq)
        self.assertTrue(element in self.seq)

    def test_sample(self):
        with self.assertRaises(ValueError):
            random.sample(self.seq, 20)
        for element in random.sample(self.seq, 5):
            self.assertTrue(element in self.seq)

if __name__ == '__main__':
    unittest.main()

但我从 linux2 上的 python 2.7.2 [GCC 4.1.2 20080704 (Red Hat 4.1.2-51)] 收到此错误消息：

.E.
======================================================================
ERROR: test_sample (__main__.TestSequenceFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tmp.py", line 23, in test_sample
    with self.assertRaises(ValueError):
TypeError: failUnlessRaises() takes at least 3 arguments (2 given)

----------------------------------------------------------------------
Ran 3 tests in 0.001s

FAILED (errors=1)

如何让assertRaises() 正常工作？

Answer 1

在 python 2.7 中添加了使用 unittest.TestCase.AssertRaises() 作为上下文管理器的功能。 http://docs.python.org/2/library/unittest.html#unittest.TestCase.assertRaises

Answer 2

检查你是否真的在使用 2.7 python。

使用pythonbrew 测试：

$ pythonbrew use 2.7.2
$ python test.py 
...
----------------------------------------------------------------------
Ran 3 tests in 0.000s

OK
$ pythonbrew use 2.6.5
$ python test.py
.E.
======================================================================
ERROR: test_sample (__main__.TestSequenceFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test.py", line 23, in test_sample
    with self.assertRaises(ValueError):
TypeError: failUnlessRaises() takes at least 3 arguments (2 given)

----------------------------------------------------------------------
Ran 3 tests in 0.000s

FAILED (errors=1)

Answer 3

如果您使用的是 2.7 并且仍然遇到此问题，可能是因为您没有使用 python 的 unittest 模块。 twisted 等其他一些模块提供了assertRaises，尽管它们试图保持与 python 的 unittest 的兼容性，但您的该模块的特定版本可能已经过时了。