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[TOC]

![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/7cd47362-951c-11ee-986a-0242ac110004.png)
# 一、Python中为False的数值断言均失败
在Python语言中表示False的数值即各个数据类型的空值，如整数的0，字符串的空字符串，None值，空列表、空字典、空集合、空元组，布尔类型的False等，这里需要注意的是一个空格的字符串的值不是False，编写测试脚本如下
```bash
def test_demo01():
    assert 0

def test_demo02():
    assert 0.0

def test_demo03():
    assert ""

def test_demo04():
    assert ()

def test_demo05():
    assert {}

def test_demo06():
    assert []

def test_demo07():
    assert None

def test_demo08():
    assert False

def test_demo09():
    assert " "

```
执行结果如下，可以看出有8个用例失败，有1个用例通过，通过的那个用例即对空格字符串的判断，即空格字符串的布尔值是True，而空字符串的布尔值则是False。

```bash
$ pytest
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.13, pytest-7.1.2, pluggy-1.0.0
rootdir: G:\redrose2100_book\ebooks\Pytest企业级应用实战\src
collected 9 items

test_demo.py FFFFFFFF.                                                                                                                                            [100%]

=============================================================================== FAILURES =============================================================================== 
_____________________________________________________________________________ test_demo01 ______________________________________________________________________________

def test_demo01():
>       assert 0
E       assert 0

test_demo.py:2: AssertionError
_____________________________________________________________________________ test_demo02 ______________________________________________________________________________

def test_demo02():
>       assert 0.0
E       assert 0.0

test_demo.py:5: AssertionError
_____________________________________________________________________________ test_demo03 ______________________________________________________________________________

def test_demo03():
>       assert ""
E       AssertionError: assert ''

test_demo.py:8: AssertionError
_____________________________________________________________________________ test_demo04 ______________________________________________________________________________

def test_demo04():
>       assert ()
E       assert ()

test_demo.py:11: AssertionError
_____________________________________________________________________________ test_demo05 ______________________________________________________________________________

def test_demo05():
>       assert {}
E       assert {}

test_demo.py:14: AssertionError
_____________________________________________________________________________ test_demo06 ______________________________________________________________________________

def test_demo06():
>       assert []
E       assert []

test_demo.py:17: AssertionError
_____________________________________________________________________________ test_demo07 ______________________________________________________________________________

_____________________________________________________________________________ test_demo08 ______________________________________________________________________________

def test_demo08():
>       assert False
E       assert False

test_demo.py:23: AssertionError
======================================================================= short test summary info ======================================================================== 
FAILED test_demo.py::test_demo01 - assert 0
FAILED test_demo.py::test_demo02 - assert 0.0
FAILED test_demo.py::test_demo03 - AssertionError: assert ''
FAILED test_demo.py::test_demo04 - assert ()
FAILED test_demo.py::test_demo05 - assert {}
FAILED test_demo.py::test_demo06 - assert []
FAILED test_demo.py::test_demo07 - assert None
FAILED test_demo.py::test_demo08 - assert False
===================================================================== 8 failed, 1 passed in 0.16s ======================================================================
```
# 二、Python逻辑表达式为False的断言均失败
在Python中常用的逻辑判断表达式，比如==、！=、<、>、<=、>=、is、is not，in，not in，is None，is not None等，断言时均失败，编写测试用例代码如下
```bash
def test_demo01():
    assert 1==2

def test_demo02():
    assert 3<2

def test_demo03():
    assert 3 is str

def test_demo04():
    assert 3 in [1,2,4]

def test_demo05():
    assert 0 is None

```

执行结果如下,即五个测试用例均失败。
```bash
pytest
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.13, pytest-7.1.2, pluggy-1.0.0
rootdir: G:\redrose2100_book\ebooks\Pytest企业级应用实战\src
collected 5 items

test_demo.py FFFFF                                                                                                                                                [100%]

def test_demo01():
>       assert 1==2
E       assert 1 == 2

test_demo.py:2: AssertionError
_____________________________________________________________________________ test_demo02 ______________________________________________________________________________

def test_demo02():
>       assert 3<2
E       assert 3 < 2

test_demo.py:5: AssertionError
_____________________________________________________________________________ test_demo03 ______________________________________________________________________________

def test_demo03():
test_demo.py:11: AssertionError
_____________________________________________________________________________ test_demo05 ______________________________________________________________________________

def test_demo05():
>       assert 0 is None
E       assert 0 is None

test_demo.py:14: AssertionError
======================================================================= short test summary info ======================================================================== 
FAILED test_demo.py::test_demo01 - assert 1 == 2
FAILED test_demo.py::test_demo02 - assert 3 < 2
FAILED test_demo.py::test_demo03 - assert 3 is str
FAILED test_demo.py::test_demo04 - assert 3 in [1, 2, 4]
FAILED test_demo.py::test_demo05 - assert 0 is None
========================================================================== 5 failed in 0.14s ===========================================================================
```
在Pytest中，断言assert语句的使用就是这么简单，主要看assert后的数值或者表达式的布尔值，如果为True，则用例通过，如果为False，则用例失败。

# 三、自定义断言报错信息
在自定义断言报错信息之前，首先观察一下默认的情况的报错信息，编写测试代码如下就
```bash
def test_demo():
    a=5
    assert a==10
```
执行结果如下，仔细观察也是能看出来错误原因的，只不过我们测试人员都是追求极致的简单，希望一样就能看出错误的原因。
```bash
$ pytest
========================================================================= test session starts ========================================================================== 
platform win32 -- Python 3.9.13, pytest-7.1.2, pluggy-1.0.0
rootdir: G:\redrose2100_book\ebooks\Pytest企业级应用实战\src
collected 1 item

test_demo.py F                                                                                                                                                    [100%]

=============================================================================== FAILURES =============================================================================== 
______________________________________________________________________________ test_demo _______________________________________________________________________________

def test_demo():
        a=5
>       assert a==10
E       assert 5 == 10

test_demo.py:3: AssertionError
======================================================================= short test summary info ======================================================================== 
FAILED test_demo.py::test_demo - assert 5 == 10
========================================================================== 1 failed in 0.11s =========================================================================== 
```
编写如下代码
```bash
def test_demo():
    a=5
    assert a==10 , "变量a期望是10，当前为%d" % a

```
执行结果如下，可以很快的从断言报错信息中看出断言失败的原因，即“变量a的值期望的是10，当前为5”，这样一来对自动化脚本调试和执行时定位问题等非常方便。
```bash
$ pytest
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.13, pytest-7.1.2, pluggy-1.0.0
rootdir: G:\redrose2100_book\ebooks\Pytest企业级应用实战\src
collected 1 item

test_demo.py F                                                                                                                                                    [100%]

=============================================================================== FAILURES =============================================================================== 
______________________________________________________________________________ test_demo _______________________________________________________________________________

def test_demo():
        a=5
>       assert a==10 , "变量a期望是10，当前为%d" % a
E       AssertionError: 变量a期望是10，当前为5
E       assert 5 == 10

test_demo.py:3: AssertionError
======================================================================= short test summary info ======================================================================== 
FAILED test_demo.py::test_demo - AssertionError: 变量a期望是10，当前为5
========================================================================== 1 failed in 0.11s ===========================================================================
```

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