[英]How can I wrap unittest's assertRaises in another context manager?
[英]Using a context manager with Python assertRaises
unittest
的Python文檔暗示assertRaises()
方法可以用作上下文管理器。 下面的代碼給出了一個Python文檔中單元測試的簡單示例。 testsample()
方法中的assertRaises()
調用工作正常。
現在我想在引發異常時訪問它,但是如果我將它注釋掉,而是取消注釋我嘗試使用上下文管理器的下一個塊,當我嘗試執行代碼時,我得到一個AttributeError: __exit__
。 這適用於Python 2.7.2和3.2.2。 我可以try...except
捕獲異常try...except
塊並以這種方式訪問它,但是單元測試的文檔似乎意味着上下文管理器也會這樣做。
還有別的我在這里做錯了嗎?
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()
似乎沒有人提出:
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作為exception_context_manager的縮寫。
unittest的源代碼沒有顯示assertRaises的異常鈎子:
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,正如您所懷疑的那樣,如果您想要在保持assertRaises測試的同時攔截異常,那么構建您自己的try / except塊是可行的方法:
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
根據文件:
如果使用省略的callableObj或None調用,則返回上下文對象
所以代碼應該是:
with self.assertRaises(ValueError):
random.sample(self.seq, 20)
考慮到這是六年前的問題,我想這是現在有效但當時沒有用的東西。 文檔說明這出現在2.7但不是微版本。
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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