如何正确断言在pytest中引发异常？

Question

码:

# 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,所以我会看到whatever函数中引发异常的位置？

Answer 1

pytest.raises(Exception) 是你需要的.

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

产量

============================================================================================= 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保存异常对象以便从中提取详细信息.例如,如果要检查异常调用堆栈或其他嵌套异常.

Answer 2

你的意思是这样的:

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'

Answer 3

在pytest中有两种处理这种情况的方法:

• 使用pytest.raises功能

• 使用pytest.mark.xfail装饰

用法pytest.raises:

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

用法pytest.mark.xfail:

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

产量pytest.raises:

============================= 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标记输出:

============================= 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=============================

正如文件所说:

pytest.raises对于您正在测试自己的代码故意提出的异常的情况,使用可能会更好,而使用@pytest.mark.xfailcheck函数可能更适合记录未修复的错误(测试描述应该发生什么)或依赖项中的错误.

Answer 4

你可以试试

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

Answer 5

处理异常的方法有两种pytest：

1. 用于pytest.raises编写有关引发异常的断言
2. 使用@pytest.mark.xfail

1. 使用pytest.raises

来自文档：

为了编写有关引发异常的断言，您可以使用pytest.raises上下文管理器

例子：

仅断言一个例外：

import pytest


def test_zero_division():
    with pytest.raises(ZeroDivisionError):
        1 / 0

with pytest.raises(ZeroDivisionError)表示下一个代码块中的任何内容都应该引发ZeroDivisionError异常。如果没有引发异常，则测试失败。如果测试引发不同的异常，则测试失败。

如果您需要访问实际的异常信息：

import pytest

def f():
    f()

def test_recursion_depth():
    with pytest.raises(RuntimeError) as excinfo:
        f()
    assert "maximum recursion" in str(excinfo.value)

excinfo是一个ExceptionInfo实例，它是引发的实际异常的包装器。感兴趣的主要属性是.type、.value和.traceback。

2. 使用@pytest.mark.xfail

也可以指定一个raises参数pytest.mark.xfail。

import pytest

@pytest.mark.xfail(raises=IndexError)
def test_f():
    l = [1, 2, 3]
    l[10]

@pytest.mark.xfail(raises=IndexError)表示下一个代码块中的任何内容都应该引发IndexError异常。如果IndexError引发了，则测试标记为xfailed (x)。如果没有引发异常，则测试标记为xpassed (X)。如果测试引发不同的异常，则测试失败。

笔记：

• 对于测试您自己的代码故意引发的异常的情况，使用pytest.raises可能会更好，而@pytest.mark.xfail对于记录未修复的错误或依赖项中的错误等情况，与检查函数一起使用可能会更好。

• 您可以将match关键字参数传递给上下文管理器 ( pytest.raises) 以测试正则表达式是否与异常的字符串表示形式匹配。（查看更多）

Answer 6

pytest不断发展，并且随着最近的一次不错的变化，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：

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

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。

Answer 7

我们正在使用这个解决方案：

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

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

Answer 8

正确的方法正在使用，pytest.raises但我在这里的评论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使用：

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