如何正确断言在 pytest 中引发异常? [英] How to properly assert that an exception gets raised in pytest?
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问题描述
# 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:
================================ 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 ==============================
如何使 pytest 打印回溯,以便我可以查看 whatever
函数中的何处引发异常?
How to make pytest print traceback, so I would see where in the whatever
function an exception was raised?
推荐答案
pytest.raises(Exception)
正是你所需要的.
pytest.raises(Exception)
is what you need.
代码
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
输出
============================================================================================= 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
会保存异常对象,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.
Note that e_info
saves the exception object so you can extract details from it. For example, if you want to check the exception call stack or another nested exception inside.
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