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[TOC]

![](https://redrose2100.oss-cn-hangzhou.aliyuncs.com/img/7cd47362-951c-11ee-986a-0242ac110004.png)

## 一、什么是fixture
pytest的fixture，就是pytest在执行测试用例函数的时候，先去看测试函数的形参，然后去fixture中找是否有名字匹配的，如果有，则去执行fixture函数的内容，并且根据fixture函数的返回值情况，比如fixture函数有返回值，则会将此返回值传递给测试函数，作为此测试函数中当前形参的实参值传入，声明一个fixture函数只需要在函数定义上面增加@pytest.fixture()声明即可
## 二、fixture类似函数传值
如下，首先声明了一个fixture函数get_num，这里为了简单的演示其作用，这是打印了一行语句，然后就返回一个数字10，在实际应用中，这里可以做很复杂的处理。当pytest执行测试函数test_func的时候，首先看一下形参，这里比如get_num，然后pytest就去自己的fixture函数列表中找是否有同名的，这里发现有，于是就去执行get_num函数，此外发现get_num这个fixture函数有一个返回值10，于是就将这个返回值10拿过来赋值给当前作为参数形参的get_num的值，这也就是为什么在测试函数中可以直接使用get_num进行断言的原因

test_demo.py代码如下
```python
import pytest

@pytest.fixture()
def get_num():
    print("\nin get_num fixture...")
    return 10

def test_func(get_num):
    assert get_num == 9
```
执行结果如下：
```bash
$ pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 1 item

test_demo.py
in get_num fixture...
F

=============================================================================== FAILURES ===============================================================================
______________________________________________________________________________ test_func _______________________________________________________________________________

get_num = 10

def test_func(get_num):
>       assert get_num == 9
E       assert 10 == 9

test_demo.py:9: AssertionError
======================================================================= short test summary info ========================================================================
FAILED test_demo.py::test_func - assert 10 == 9
========================================================================== 1 failed in 0.10s ===========================================================================

```

## 三、fixture中继续调用fixture
如下，get_num2的fixture中继续调用了get_num1的fixture，然后测试函数中调用get_num2的fixture，原理都是一样大金额

test_demo.py代码如下：
```python
import pytest

@pytest.fixture()
def get_num1():
    print("\nin get_num1 fixture...")
    return 100

@pytest.fixture()
def get_num2(get_num1):
    print("\nin get_num2 fixture...")
    return 10+get_num1

def test_func(get_num2):
    assert get_num2 == 111
```
执行结果如下
```bash
$ pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 1 item

test_demo.py
in get_num1 fixture...

in get_num2 fixture...
F

get_num2 = 110

def test_func(get_num2):
>       assert get_num2 == 111
E       assert 110 == 111

test_demo.py:14: AssertionError
======================================================================= short test summary info ========================================================================
FAILED test_demo.py::test_func - assert 110 == 111
========================================================================== 1 failed in 0.10s ===========================================================================

```
## 四、测试函数同时可以调用多个fixture
如下，test_func测试函数中调用了两个fixture

test_demo.py代码如下
```python
import pytest

@pytest.fixture()
def get_num1():
    print("\nin get_num1 fixture...")
    return 100

@pytest.fixture()
def get_num2():
    print("\nin get_num2 fixture...")
    return 200

def test_func(get_num1,get_num2):
    assert int(get_num1+get_num2) == 301
```
执行结果如下
```bash
$ pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 1 item

test_demo.py
in get_num1 fixture...

in get_num2 fixture...
F

get_num1 = 100, get_num2 = 200

def test_func(get_num1,get_num2):
>       assert int(get_num1+get_num2) == 301
E       assert 300 == 301
E        +  where 300 = int((100 + 200))

test_demo.py:14: AssertionError
======================================================================= short test summary info ========================================================================
FAILED test_demo.py::test_func - assert 300 == 301
========================================================================== 1 failed in 0.10s ===========================================================================

```
## 五、fixture可以设置自动执行
在定义fixture函数的时候，通过将autouse设置为True即可，如下所示，虽然整个过程中都没有调用init_name这个fixture，但是通过最后执行的结果看，这个init_name的fixture明显是执行了的

test_demo.py如下
```python
import pytest

@pytest.fixture()
def get_name():
    print("\nin get_name fixture...")
    return []

@pytest.fixture(autouse=True)
def init_name(get_name):
    print("\nin init fixture...")
    get_name.append("张无忌")
    get_name.append("张三丰")

def test_func(get_name):
    assert "周芷若" in get_name
```
执行结果如下
```bash
$ pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 1 item

test_demo.py
in get_name fixture...

in init fixture...
F

get_name = ['张无忌', '张三丰']

def test_func(get_name):
>       assert "周芷若" in get_name
E       AssertionError: assert '周芷若' in ['张无忌', '张三丰']

test_demo.py:15: AssertionError
======================================================================= short test summary info ========================================================================
FAILED test_demo.py::test_func - AssertionError: assert '周芷若' in ['张无忌', '张三丰']
========================================================================== 1 failed in 0.11s ===========================================================================

```
## 六、fixture的范围
在此之前介绍额fixture似乎都是在传递值，像调用函数一样，其实传递值只是fixture的一个很小的应用，fixture最重要的作用是充当类似其他测试框架中的setup和teardown，通过上述的介绍可以得出的一个结论就是，通过调用fixture，可以做到fixture函数的代码是在测试函数之前执行的，试想，如果fixture函数的代码是比如初始化环境的代码，那么此时fixture的作用就完全可以理解为自动化测试用例的setup步骤了，事实上也确实如此，pytest自动化框架确实是fixture中的代码执行认为是setup和teardown的步骤的。

因此当把fixture作为充当setup和teardown的作用，那么问题就来了，setup和teardown是有测试函数级setup和teardown，测试类级setup和teardown，测试模块级setup和teardown，以及整个测试执行最开始和最后的setup和teardown，理解到此，就可以理解fixture的范围了，fixture的范围有以下几个：
* function: 测试函数级，这个是fixture默认的范围，如果不设置即为function级别fixture

* class: 测试类级的fixture

* module: 测试模块级的fixture

* package: 测试包级别的fixture

* session: 翻译过来叫会话级别的fixture，一个会话实质上就是执行pytest命令的整个过程，即session级实质上就是执行pytest最开始和最后的setup和teardown

session，module，package级额fixture一般在conftest.py中定义，其他级别的fixture可以在conftest.py中定义也可以在具体文件中定义，如果是共享给其他文件使用则放在conftest.py中定义，如果是自己文件中独有的，则在自己的文件中定义即可

如下，conftest.py中定义session级的fixture
```python
import pytest

@pytest.fixture(autouse=True,scope="session")
def session_fixture():
    print("\nin session_fixture...")
```
test_demo.py中定义function级别的fixture
```python
import pytest

@pytest.fixture(autouse=True,scope="function")
def function_fixture():
    print("\nin function_fixture...")

def test_func1():
    print("in test_func1...")

def test_func2():
    print("in test_func2...")

def test_func3():
    print("in test_func3...")
```
执行结果如下，可以看到session即的只会在最开始执行一次，而function级的则会在每个测试好桉树之前都会执行，这就做到了setup的功能，至于teardown的功能需要使用到yield关键字，后续继续展开
```bash
$ pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 3 items

test_demo.py
in session_fixture...

in function_fixture...
in test_func1...
.
in function_fixture...
in test_func2...
.
in function_fixture...
in test_func3...
.

========================================================================== 3 passed in 0.02s ===========================================================================

```
## 七、fixture通过yield关键字实现setup和teardown
fixture中，yield关键字之前的代码为setup的步骤，yield之后的代码即为teardown的步骤，yield相当于return，如果有返回值，就直接放在yield，如果没有返回值则直接使用yield即可

如conftest.py中如下：
```python
import pytest

@pytest.fixture(autouse=True,scope="session")
def session_fixture():
    print("\nin session_fixture setup ...")
    yield
    print("\nin session_fixture teardown ...")
```
test_demo.py中如下：
```python
import pytest

@pytest.fixture(autouse=True,scope="function")
def function_fixture():
    print("\nin function_fixture setup ...")
    yield 10
    print("\nin function_fixture teardown ...")

def test_func1():
    print("in test_func1...")

def test_func2():
    print("in test_func2...")

def test_func3(function_fixture):
    print("in test_func3...")
    assert function_fixture == 11
```
执行结果如下，此时已经实现了setup和teardown的功能，此外function级的fixture还返回了一个数值
```bash
$ pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 3 items

test_demo.py
in session_fixture setup ...

in function_fixture setup ...
in test_func1...
.
in function_fixture teardown ...

in function_fixture setup ...
in test_func2...
.
in function_fixture teardown ...

in function_fixture setup ...
in test_func3...
F
in function_fixture teardown ...

in session_fixture teardown ...

=============================================================================== FAILURES ===============================================================================
______________________________________________________________________________ test_func3 ______________________________________________________________________________

function_fixture = 10

def test_func3(function_fixture):
        print("in test_func3...")
>       assert function_fixture == 11
E       assert 10 == 11

test_demo.py:17: AssertionError
======================================================================= short test summary info ========================================================================
FAILED test_demo.py::test_func3 - assert 10 == 11
===================================================================== 1 failed, 2 passed in 0.10s ======================================================================

```
## 八、yield的缺陷及解决方案
首先看下如下例子，test_demo.py内容如下：
```python
import pytest

@pytest.fixture(autouse=True,scope="function")
def function_fixture():
    print("\nin function_fixture setup ...")
    a=1/0
    yield 10
    print("\nin function_fixture teardown ...")

def test_func3(function_fixture):
    print("in test_func3...")
    assert function_fixture == 11
```
执行结果如下，仔细观察就会发现，当在setup部分出错了，则teardown部分根本就不会执行了，这一点对于自动化测试来讲是有一定弊端的，比如在setup部分配置了一些基础数据，然后由于某种原因出错了，这样由于根本不会执行teardown的操作，从而导致整体环境就有残留了，这就是yield关键字存在的弊端
```bash
$ pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 1 item

test_demo.py
in function_fixture setup ...
E

================================================================================ ERRORS ================================================================================
_____________________________________________________________________ ERROR at setup of test_func3 _____________________________________________________________________

@pytest.fixture(autouse=True,scope="function")
    def function_fixture():
        print("\nin function_fixture setup ...")
>       a=1/0
E       ZeroDivisionError: division by zero

test_demo.py:6: ZeroDivisionError
======================================================================= short test summary info ========================================================================
ERROR test_demo.py::test_func3 - ZeroDivisionError: division by zero
=========================================================================== 1 error in 0.10s ===========================================================================

```
如下，通过request的addfinalizer则可以解决这个问题

test_demo.py内容如下：
```python
import pytest

@pytest.fixture(autouse=True,scope="function")
def function_fixture(request):

def teardown_op():
        print("\nin function_fixture teardown ...")
    request.addfinalizer(teardown_op)
    print("\nin function_fixture setup ...")
    a=10/0
    return 10

def test_func3(function_fixture):
    print("in test_func3...")
    assert function_fixture == 11
```
执行结果如下，可以发现虽然setup部分虽然出错了，但是teardown仍然可以正常执行
```bash
pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 1 item

test_demo.py
in function_fixture setup ...
E
in function_fixture teardown ...

request = <SubRequest 'function_fixture' for <Function test_func3>>

@pytest.fixture(autouse=True,scope="function")
    def function_fixture(request):

def teardown_op():
            print("\nin function_fixture teardown ...")
        request.addfinalizer(teardown_op)
        print("\nin function_fixture setup ...")
>       a=10/0
E       ZeroDivisionError: division by zero

test_demo.py:10: ZeroDivisionError
======================================================================= short test summary info ========================================================================
ERROR test_demo.py::test_func3 - ZeroDivisionError: division by zero
=========================================================================== 1 error in 0.10s ===========================================================================

```
上面的优化能解决teardown不执行的问题，但是还有另外的问题，比如setup有5个步骤，teardown有对应的5个步骤，则按照上面的解决办法带来一个问题是比如setup中在第二个步骤中报错了，则此时相当于setup只成功执行了一个步骤，而上述解决方案中的teardown中不得不把5个步骤全部执行，这在一些场景中也是有问题的

为了解决上面的问题，下面的解决方案则可能稍微更好一些，即还是使用yield关键字，不过每一个fixture的setup只做原子操作，teardown也只做与setup对应的原子操作，如下代码中f1，f2，f3中的setup和teardown分别只做原子操作，假设在f2的setup中由于某种原因出错，此时f2因为setup报错了，因此f2没有必要执行teardown，而采用这种方案即使f2中setup失败了，f1的teardown仍然执行，如此则达到了只要setup成功了就会执行其对应的teardown操作

如下test_demo.py代码如下：
```python
import pytest

@pytest.fixture(scope="function")
def f1():
    print("\nin f1 fixture setup...")
    yield
    print("\nin f1 fixture teardown...")

@pytest.fixture(scope="function")
def f2(f1):
    print("\nin f2 fixture setup...")
    a=1/0
    yield
    print("\nin f2 fixture teardown...")

@pytest.fixture(scope="function")
def f3(f2):
    print("\nin f3 fixture setup...")
    yield 10
    print("\nin f3 fixture teardown...")

def test_func3(f3):
    print("\nin test_func3...")
    assert f3 == 11
```
执行结果如下：
```bash
$ pytest -s
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: D:\src\blog\tests, configfile: pytest.ini
plugins: allure-pytest-2.9.43, caterpillar-pytest-0.0.2, hypothesis-6.31.6, forked-1.3.0, rerunfailures-10.1, xdist-2.3.0
collected 1 item

test_demo.py
in f1 fixture setup...

in f2 fixture setup...
E
in f1 fixture teardown...

f1 = None

@pytest.fixture(scope="function")
    def f2(f1):
        print("\nin f2 fixture setup...")
>       a=1/0
E       ZeroDivisionError: division by zero

test_demo.py:12: ZeroDivisionError
======================================================================= short test summary info ========================================================================
ERROR test_demo.py::test_func3 - ZeroDivisionError: division by zero
=========================================================================== 1 error in 0.10s ===========================================================================

```

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