Question

<代码>unittest的 Python文件意味着assertRaises()方法可用作背景管理人。下面的法典提供了从Adhury docs中进行单位测试的简单例子。 <assertRaises(>> calls in the testsample(> methods workvy.

现在,在提出这一例外时,我就同意这一例外,但如果我对它发表评论,而不是对我试图利用一名环境主管的下一个障碍作出结论,我就有一个<条码>。 AttributeError: __exit__, 当我试图执行该守则时。发生这种情况的有2.7.2和3.2.2。我可以在<条码>栏中捕获这一例外情况,但栏目除外,并且以这种方式查阅,但用于单位测试的文件似乎也意味着环境主管也将这样做。

这里还有什么事情是错的?

class TestSequenceFunctions(unittest.TestCase):

    def setUp(self):
        self.seq = [x for x in range(10)]

    def testshuffle(self):
        # make sure the shuffled sequence does not lose any elements
        random.shuffle(self.seq)
        self.seq.sort()
        self.assertEqual(self.seq, [x for x in range(10)])

    def testchoice(self):
        element = random.choice(self.seq)
        self.assert_(element in self.seq)

    def testsample(self):
        self.assertRaises(ValueError, random.sample, self.seq, 20)

        # with self.assertRaises(ValueError, random.sample, self.seq, 20):
        #     print("Inside cm")

        for element in random.sample(self.seq, 5):
            self.assert_(element in self.seq)

if __name__ ==  __main__ :
    unittest.main()

Answer 1

The source code for unittest doesn t show an exception hook for assertRaises:

class _AssertRaisesContext(object):
    """A context manager used to implement TestCase.assertRaises* methods."""

    def __init__(self, expected, test_case, expected_regexp=None):
        self.expected = expected
        self.failureException = test_case.failureException
        self.expected_regexp = expected_regexp

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, tb):
        if exc_type is None:
            try:
                exc_name = self.expected.__name__
            except AttributeError:
                exc_name = str(self.expected)
            raise self.failureException(
                "{0} not raised".format(exc_name))
        if not issubclass(exc_type, self.expected):
            # let unexpected exceptions pass through
            return False
        self.exception = exc_value # store for later retrieval
        if self.expected_regexp is None:
            return True

        expected_regexp = self.expected_regexp
        if isinstance(expected_regexp, basestring):
            expected_regexp = re.compile(expected_regexp)
        if not expected_regexp.search(str(exc_value)):
            raise self.failureException( "%s" does not match "%s"  %
                     (expected_regexp.pattern, str(exc_value)))
        return True

因此,正如你所怀疑的那样,如果你想要在坚持主张的同时拦截该例外,就行走。噪音试验:

def testsample(self):
    with self.assertRaises(ValueError):
         try:
             random.sample(self.seq, 20)
         except ValueError as e:
             # do some action with e
             self.assertEqual(e.args,
                              ( sample larger than population ,))
             # now let the context manager do its work
             raise

Answer 2

似乎没有人建议:

import unittest
# For python < 2.7, do import unittest2 as unittest

class Class(object):
    def should_raise(self):
        raise ValueError( expected arg )

class test_Class(unittest.TestCase):
    def test_something(self):
        DUT = Class()
        with self.assertRaises(ValueError) as exception_context_manager:
            DUT.should_raise()
        exception = exception_context_manager.exception

        self.assertEqual(exception.args, ( expected arg , ))

我通常使用e_cm作为例外使用:context_manager。

Answer 3

根据文件:

如果用可召唤的Obj漏掉或无,将退回背景物体

因此,该法典应当:

with self.assertRaises(ValueError):
    random.sample(self.seq, 20)

Answer 4

鉴于6年前有人问这个问题,我想象,这是现在行之有效的,但当时却不做。 docs 这一点在2.7中出现,但不是微观版本。

import unittest

class TestIntParser(unittest.TestCase):

    def test_failure(self):
        failure_message =  invalid literal for int() with base 10 
        with self.assertRaises(ValueError) as cm:
            int( forty two )
        self.assertIn(failure_message, cm.exception.message)

if __name__ ==  __main__ :
    unittest.main()

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