关于python：如何正确断言pytest中引发了异常？

How to properly assert that an exception gets raised in pytest?

码：

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# coding=utf-8
import pytest

def whatever():
return 9/0

def test_whatever():
try:
whatever()
except ZeroDivisionError as exc:
pytest.fail(exc, pytrace=True)

输出：

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================================ test session starts =================================
platform linux2 -- Python 2.7.3 -- py-1.4.20 -- pytest-2.5.2
plugins: django, cov
collected 1 items

pytest_test.py F

====================================== FAILURES ======================================
___________________________________ test_whatever ____________________________________

def test_whatever():
try:
whatever()
except ZeroDivisionError as exc:
> pytest.fail(exc, pytrace=True)
E Failed: integer division or modulo by zero

pytest_test.py:12: Failed
============================== 1 failed in 1.16 seconds ==============================

如何进行pytest打印回溯，所以我会看到在whatever函数的何处引发了异常？

相关讨论

pytest.raises(Exception)是您所需要的。

码

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import pytest

def test_passes():
with pytest.raises(Exception) as e_info:
x = 1 / 0

def test_passes_without_info():
with pytest.raises(Exception):
x = 1 / 0

def test_fails():
with pytest.raises(Exception) as e_info:
x = 1 / 1

def test_fails_without_info():
with pytest.raises(Exception):
x = 1 / 1

# Don't do this. Assertions are caught as exceptions.
def test_passes_but_should_not():
try:
x = 1 / 1
assert False
except Exception:
assert True

# Even if the appropriate exception is caught, it is bad style,
# because the test result is less informative
# than it would be with pytest.raises(e)
# (it just says pass or fail.)

def test_passes_but_bad_style():
try:
x = 1 / 0
assert False
except ZeroDivisionError:
assert True

def test_fails_but_bad_style():
try:
x = 1 / 1
assert False
except ZeroDivisionError:
assert True

产量

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============================================================================================= test session starts ==============================================================================================
platform linux2 -- Python 2.7.6 -- py-1.4.26 -- pytest-2.6.4
collected 7 items

test.py ..FF..F

=================================================================================================== FAILURES ===================================================================================================
__________________________________________________________________________________________________ test_fails __________________________________________________________________________________________________

def test_fails():
with pytest.raises(Exception) as e_info:
> x = 1 / 1
E Failed: DID NOT RAISE

test.py:13: Failed
___________________________________________________________________________________________ test_fails_without_info ____________________________________________________________________________________________

def test_fails_without_info():
with pytest.raises(Exception):
> x = 1 / 1
E Failed: DID NOT RAISE

test.py:17: Failed
___________________________________________________________________________________________ test_fails_but_bad_style ___________________________________________________________________________________________

def test_fails_but_bad_style():
try:
x = 1 / 1
> assert False
E assert False

test.py:43: AssertionError
====================================================================================== 3 failed, 4 passed in 0.02 seconds ======================================================================================

请注意，e_info保存异常对象，以便您可以从中提取详细信息。例如，如果要检查异常调用堆栈或内部的另一个嵌套异常。

相关讨论

您的意思是这样的吗：

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def test_raises():
with pytest.raises(Exception) as excinfo:
raise Exception('some info')
# these asserts are identical; you can use either one
assert execinfo.value.args[0] == 'some info'
assert str(execinfo.value) == 'some info'

相关讨论

有两种方法可以在pytest中处理此类情况：

使用pytest.raises函数
使用pytest.mark.xfail装饰器

pytest.raises的用法：

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def whatever():
return 9/0
def test_whatever():
with pytest.raises(ZeroDivisionError):
whatever()

pytest.mark.xfail的用法：

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@pytest.mark.xfail(raises=ZeroDivisionError)
def test_whatever():
whatever()

pytest.raises的输出：

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============================= test session starts ============================
platform linux2 -- Python 2.7.10, pytest-3.2.3, py-1.4.34, pluggy-0.4.0 --
/usr/local/python_2.7_10/bin/python
cachedir: .cache
rootdir: /home/user, inifile:
collected 1 item

test_fun.py::test_whatever PASSED

======================== 1 passed in 0.01 seconds =============================

pytest.xfail标记的输出：

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============================= test session starts ============================
platform linux2 -- Python 2.7.10, pytest-3.2.3, py-1.4.34, pluggy-0.4.0 --
/usr/local/python_2.7_10/bin/python
cachedir: .cache
rootdir: /home/user, inifile:
collected 1 item

test_fun.py::test_whatever xfail

======================== 1 xfailed in 0.03 seconds=============================

如文档所述：

Using pytest.raises is likely to be better for cases where you are testing exceptions your own code is deliberately raising, whereas using @pytest.mark.xfail with a check function is probably better for something like documenting unfixed bugs (where the test describes what"should" happen) or bugs in dependencies.

你可以试试

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def test_exception():
with pytest.raises(Exception) as excinfo:
function_that_raises_exception()
assert str(excinfo.value) == 'some info'

相关讨论

pytest不断发展，并且随着最近的一次重大变化，现在可以同时测试

异常类型(严格测试)
错误消息(使用正则表达式进行严格检查或宽松检查)

文档中的两个示例：

1 2	with pytest.raises(ValueError, match='must be 0 or None'): raise ValueError('value must be 0 or None')

1 2	with pytest.raises(ValueError, match=r'must be \d+$'): raise ValueError('value must be 42')

我已经在许多项目中使用了这种方法，并且非常喜欢它。

正确的方法是使用pytest.raises，但我在这里的注释中找到了有趣的替代方法，并希望将其保存以供将来该问题的读者参考：

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try:
thing_that_rasises_typeerror()
assert False
except TypeError:
assert True

该解决方案是我们正在使用的解决方案：

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def test_date_invalidformat():
"""
Test if input incorrect data will raises ValueError exception
"""
date ="06/21/2018 00:00:00"
with pytest.raises(ValueError):
app.func(date) #my function to be tested

请参阅pytest，https：//docs.pytest.org/en/latest/reference.html#pytest-raises

更好的做法是使用继承unittest.TestCase并运行self.assertRaises的类。

例如：

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import unittest

def whatever():
return 9/0

class TestWhatEver(unittest.TestCase):

def test_whatever():
with self.assertRaises(ZeroDivisionError):
whatever()

然后，您可以通过运行以下命令来执行它：

1	pytest -vs test_path

相关讨论

您是否尝试删除" pytrace = True"？

1 2	pytest.fail(exc, pytrace=True) # before pytest.fail(exc) # after

您是否尝试过使用'--fulltrace'吗？