pytest合集（6）— 固定装置/夹具fixture

一、什么是夹具 1、夹具定义和特性

fixture固定装置，也叫夹具，下文都称呼为夹具。

使用 @pytest.fixture 将一个函数标记成夹具。

夹具本质上是函数，它将在应用它的每个测试函数之前运行。

可以将夹具定义在conftest.py文件中，共享给多个测试使用。

pytest查找夹具的顺序：测试类>>测试模块>> conftest.py 文件>>内置插件和第三方插件。

附上官网说明：

pytest 夹具被设计为显式、模块化和可扩展的。

在基本层面上，测试函数通过将它们声明为参数来请求它们所需的夹具。

当 pytest 开始运行测试时，它会查看该测试函数签名中的参数，然后搜索与这些参数具有相同名称的夹具。一旦 pytest 找到它们，它就会运行这些固定装置，捕获它们返回的内容（如果有的话），并将这些对象作为参数传递给测试函数。

总结：

说了这么多，我理解的在pytest中使用夹具fixture的作用类似于unittest框架里的setup和teardown，用来管理测试用例的前置处理和后置处理。

2、夹具应用场景

测试环境搭建和销毁

数据库连接和关闭

测试数据的共享

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二、怎么用夹具

使用 @pytest.fixture 将一个函数标记成夹具。

1、将夹具名作为测试函数参数中传入

新建 test_fixture.py 文件如下：

import pytest


@pytest.fixture()
def my_fixture():
    print("this is my fixture")
    return True


def test_one(my_fixture):
    assert my_fixture is True

将夹具名 my_fixture 作为参数传入到了测试函数（测试用例）test_one中。运行命令：pytest -vs test_fixture.py

(venv) C:Users57776PycharmProjectspytest-demotestfixture>pytest -vs test_fixture.py
=================================== test session starts ===================================
platform win32 -- Python 3.8.8, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- e:programspythonpython38python.exe
cachedir: .pytest_cache
metadata: {'Python': '3.8.8', 'Platform': 'Windows-10-10.0.19041-SP0', 'Packages': {'pytest': '6.2.3', 'py': '1.10.0', 'pluggy': '0.13.1'}, 'Plugins': {'html': '3.1.
1', 'metadata': '1.11.0', 'rerunfailures': '9.1.1', 'assume': '2.2.0', 'requests-mock': '1.7.0'}, 'JAVA_HOME': 'C:\Program Files\Java\jdk1.8.0_271', 'foo': 'bar'}

rootdir: C:Users57776PycharmProjectspytest-demotestfixture
plugins: html-3.1.1, metadata-1.11.0, rerunfailures-9.1.1, assume-2.2.0, requests-mock-1.7.0
collected 1 item

test_fixture.py::test_one this is my fixture
PASSED

=================================== 1 passed in 0.06s ===================================

(venv) C:Users57776PycharmProjectspytest-demotestfixture>

说明：

pytest 运行测试函数 test_one 的时候，会先去运行它参数的同名夹具test_fixture，打印出了"this is my fixture"，并且捕获到了夹具的返回值 True。

（1）fixture运行过程探究

使用 --setup-show （注意这里是双--）命令行参数来查看fixture的执行过程。

运行命令：pytest -v --setup-show test_fixture.py

(venv) C:Users57776PycharmProjectspytest-demotestfixture>pytest -vs --setup-show test_fixture.py
==================================== test session starts ====================================
platform win32 -- Python 3.8.8, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- e:programspythonpython38python.exe
cachedir: .pytest_cache
metadata: {'Python': '3.8.8', 'Platform': 'Windows-10-10.0.19041-SP0', 'Packages': {'pytest': '6.2.3', 'py': '1.10.0', 'pluggy': '0.13.1'}, 'Plugins': {'html': '3.1.
1', 'metadata': '1.11.0', 'rerunfailures': '9.1.1', 'assume': '2.2.0', 'requests-mock': '1.7.0'}, 'JAVA_HOME': 'C:\Program Files\Java\jdk1.8.0_271', 'foo': 'bar'}

rootdir: C:Users57776PycharmProjectspytest-demotestfixture
plugins: html-3.1.1, metadata-1.11.0, rerunfailures-9.1.1, assume-2.2.0, requests-mock-1.7.0
collected 1 item

test_fixture.py::test_one this is my fixture

SETUP F my_fixture
test_fixture.py::test_one (fixtures used: my_fixture)PASSED
TEARDOWN F my_fixture

=================================== 1 passed in 0.05s ===================================

(venv) C:Users57776PycharmProjectspytest-demotestfixture>

说明：

从执行结果看到，测试函数test_one运行前执行SETUP ，运行后执行TEARDOWN。很容易联想到unittest框架中测试用例执行前后的setup和teardown操作。

2、使用conftest.py文件

如果我们有多个文件中的测试函数都使用相同的夹具，这个时候我们可以把夹具函数定义在conftest.py文件中。

新建 conftest.py文件如下：

import pytest


# 定义夹具函数
@pytest.fixture()
def my_fixture():
    print("this is my fixture")
    return True

修改 test_fixture.py 文件如下：

def test_one(my_fixture):
    assert my_fixture is True


def test_two(my_fixture):
    assert my_fixture is False

新建 test_fix.py 文件如下：

def test_three(my_fixture):
    assert 'T' in str(my_fixture)

文件目录如下：

运行命令：pytest -v 根据测试用例收集规则，pytest会运行testfixture文件夹下的所有测试用例。

(venv) C:Users57776PycharmProjectspytest-demotestfixture>pytest -v
==================================== test session starts ====================================
platform win32 -- Python 3.8.8, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- e:programspythonpython38python.exe
cachedir: .pytest_cache
metadata: {'Python': '3.8.8', 'Platform': 'Windows-10-10.0.19041-SP0', 'Packages': {'pytest': '6.2.3', 'py': '1.10.0', 'pluggy': '0.13.1'}, 'Plugins': {'html': '3.1.
1', 'metadata': '1.11.0', 'rerunfailures': '9.1.1', 'assume': '2.2.0', 'requests-mock': '1.7.0'}, 'JAVA_HOME': 'C:\Program Files\Java\jdk1.8.0_271', 'foo': 'bar'}

rootdir: C:Users57776PycharmProjectspytest-demotestfixture
plugins: html-3.1.1, metadata-1.11.0, rerunfailures-9.1.1, assume-2.2.0, requests-mock-1.7.0
collected 3 items

test_fix.py::test_three PASSED [ 33%]
test_fixture.py::test_one PASSED [ 66%]
test_fixture.py::test_two FAILED [100%]

====================================== FAILURES ======================================
_________________________________________ test_two _________________________________________

my_fixture = True

def test_two(my_fixture):
> assert my_fixture is False
E assert True is False

test_fixture.py:17: AssertionError
----------------------------------------------------------- Captured stdout setup -----------------------------------------------------------
this is my fixture
================================= short test summary info =================================
FAILED test_fixture.py::test_two - assert True is False
================================ 1 failed, 2 passed in 0.51s ================================

(venv) C:Users57776PycharmProjectspytest-demotestfixture>

说明：

从执行结果可以看到，test_fixture.py 和test_fixt.py 文件中的测试函数，在pytest运行的时候都从conftest.py文件中找到了定义的夹具my_fixture。

pytest 查找夹具顺序：测试类>>测试模块>> conftest.py 文件>>内置插件和第三方插件。

3、使用装饰器@pytest.mark.userfixtures()

语法糖：

pytest.mark.usefixtures(*args)

*args – The names of the fixture to use, as strings.

看到装饰器的参数就能晓得，usefixtures可以和一个或者多个fixture配合使用。

修改 test_fixture.py 文件如下：

import pytest


@pytest.fixture()
def my_fixture():
    print("this is my fixture")
    return True


@pytest.mark.usefixtures('my_fixture')
def test_one():
    assert my_fixture is True

运行命令：pytest -vs test_fixture.py

(venv) C:Users57776PycharmProjectspytest-demotestfixture>pytest -vs test_fixture.py
==================================== test session starts ====================================
platform win32 -- Python 3.8.8, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- e:programspythonpython38python.exe
cachedir: .pytest_cache
metadata: {'Python': '3.8.8', 'Platform': 'Windows-10-10.0.19041-SP0', 'Packages': {'pytest': '6.2.3', 'py': '1.10.0', 'pluggy': '0.13.1'}, 'Plugins': {'html': '3.1.
1', 'metadata': '1.11.0', 'rerunfailures': '9.1.1', 'assume': '2.2.0', 'requests-mock': '1.7.0'}, 'JAVA_HOME': 'C:\Program Files\Java\jdk1.8.0_271', 'foo': 'bar'}

rootdir: C:Users57776PycharmProjectspytest-demotestfixture
plugins: html-3.1.1, metadata-1.11.0, rerunfailures-9.1.1, assume-2.2.0, requests-mock-1.7.0
collected 1 item

test_fixture.py::test_one this is my fixture
FAILED

====================================== FAILURES ======================================
_________________________________________ test_one _________________________________________

@pytest.mark.usefixtures('my_fixture')
def test_one():
> assert my_fixture is True
E assert my_fixture is True

test_fixture.py:21: AssertionError
================================ short test summary info ================================
FAILED test_fixture.py::test_one - assert my_fixture is True
=================================== 1 failed in 0.49s ===================================

(venv) C:Users57776PycharmProjectspytest-demotestfixture>

说明：

从执行结果可以看到，使用这种方法并没有拿到夹具的返回值。

装饰器@pytest.mark.usefixtures是Pytest调用fixture的方法之一，与直接传入fixture不同的是，它无法获取到夹具的返回值。

这种方式的使用场景是被测试函数（测试用例）需要多个fixture的时候。

如果你想要模块中的每个测试用例都调用同一个夹具，你也可以使用pytestmark标记。

固定写法：pytestmark = pytest.mark.usefixtures("my_fixture")

修改 test_fixture.py 文件如下：

import pytest


@pytest.fixture()
def my_fixture():
    print("this is my fixture")
    return True


pytestmark = pytest.mark.usefixtures("my_fixture")


def test_one():
    assert my_fixture is True


def test_two():
    assert my_fixture is False

运行命令：pytest -vs test_fixture.py

(venv) C:Users57776PycharmProjectspytest-demotestfixture>pytest -vs test_fixture.py
================================== test session starts ==================================
platform win32 -- Python 3.8.8, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- e:programspythonpython38python.exe
cachedir: .pytest_cache
metadata: {'Python': '3.8.8', 'Platform': 'Windows-10-10.0.19041-SP0', 'Packages': {'pytest': '6.2.3', 'py': '1.10.0', 'pluggy': '0.13.1'}, 'Plugins': {'html': '3.1.
1', 'metadata': '1.11.0', 'rerunfailures': '9.1.1', 'assume': '2.2.0', 'requests-mock': '1.7.0'}, 'JAVA_HOME': 'C:\Program Files\Java\jdk1.8.0_271', 'foo': 'bar'}

rootdir: C:Users57776PycharmProjectspytest-demotestfixture
plugins: html-3.1.1, metadata-1.11.0, rerunfailures-9.1.1, assume-2.2.0, requests-mock-1.7.0
collected 2 items

test_fixture.py::test_one this is my fixture
FAILED
test_fixture.py::test_two this is my fixture
FAILED

==================================== FAILURES ====================================
_______________________________________ test_one _______________________________________

def test_one():
> assert my_fixture is True
E assert my_fixture is True

test_fixture.py:23: AssertionError
_______________________________________ test_two _______________________________________

def test_two():
> assert my_fixture is False
E assert my_fixture is False

test_fixture.py:27: AssertionError
================================ short test summary info ================================
FAILED test_fixture.py::test_one - assert my_fixture is True
FAILED test_fixture.py::test_two - assert my_fixture is False
=================================== 2 failed in 0.52s ===================================

(venv) C:Users57776PycharmProjectspytest-demotestfixture>

说明：

测试环境test_one和test_two都使用了同一个夹具my_fixture。

4、使用夹具参数autouse=TRUE

fixture夹具参数autouse ，默认值False ，则需要显式引用来激活夹具。值为TRUE的话则所有测试函数都可以使用该夹具。

修改 test_fixture.py 文件如下：

import pytest


@pytest.fixture(autouse=True)
def my_fixture():
    print("this is my fixture")
    return True


def test_one():
    assert my_fixture is True


def test_two():
    assert my_fixture is False

运行命令：pytest -vs test_fixture.py

(venv) C:Users57776PycharmProjectspytest-demotestfixture>pytest -vs test_fixture.py
================================== test session starts ==================================
platform win32 -- Python 3.8.8, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- e:programspythonpython38python.exe
cachedir: .pytest_cache
metadata: {'Python': '3.8.8', 'Platform': 'Windows-10-10.0.19041-SP0', 'Packages': {'pytest': '6.2.3', 'py': '1.10.0', 'pluggy': '0.13.1'}, 'Plugins': {'html': '3.1.
1', 'metadata': '1.11.0', 'rerunfailures': '9.1.1', 'assume': '2.2.0', 'requests-mock': '1.7.0'}, 'JAVA_HOME': 'C:\Program Files\Java\jdk1.8.0_271', 'foo': 'bar'}

rootdir: C:Users57776PycharmProjectspytest-demotestfixture
plugins: html-3.1.1, metadata-1.11.0, rerunfailures-9.1.1, assume-2.2.0, requests-mock-1.7.0
collected 2 items

test_fixture.py::test_one this is my fixture
FAILED
test_fixture.py::test_two this is my fixture
FAILED

==================================== FAILURES ====================================
_______________________________________ test_one _______________________________________

def test_one():
> assert my_fixture is True
E assert my_fixture is True

test_fixture.py:23: AssertionError
_______________________________________ test_two _______________________________________

def test_two():
> assert my_fixture is False
E assert my_fixture is False

test_fixture.py:27: AssertionError
================================ short test summary info ================================
FAILED test_fixture.py::test_one - assert my_fixture is True
FAILED test_fixture.py::test_two - assert my_fixture is False
=================================== 2 failed in 0.52s ===================================

(venv) C:Users57776PycharmProjectspytest-demotestfixture>

三、夹具的进阶用法 1、夹具中使用夹具

新建 test_append.py如下：

import pytest


@pytest.fixture
def first_entry():
    return "a"


@pytest.fixture
def order(first_entry):
    return [first_entry]


def test_string(order):
    order.append("b")
    assert order == ["a", "b"]

说明：

在夹具函数order() 中使用夹具first_entry作为参数。

2、使用多个夹具

修改test_append.py文件如下：

import pytest


@pytest.fixture
def first_entry():
    return "a"


@pytest.fixture
def second_entry():
    return 2


def test_order(first_entry, second_entry):
    assert [first_entry, second_entry] == ["a", 2]

说明：

test_order（）使用了2个夹具函数first_entry，second_entry作为参数。

reference：

Pytest - Fixtures

API Reference — pytest documentation

Fixtures reference — pytest documentation

pytest合集（6）— 固定装置/夹具fixture

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