pytest中fixture的scope

一. 定义

pytest的fixture中有一个参数scope，它的作用域有五个，分别是：function、class、module、和session

function：每个方法开始之前都会调用一次，方法级别

class：每个类开始之前都会调用一次，类级别

module：每个模块(py文件)开始之前都会调用一次，模块级别

session：一个session(多个模块)开始之前都会调用一次，包级别

二. scope="function"

定义一个test_function_scope.py，写入如下代码并运行：

import pytest

@pytest.fixture(scope="function")
def function_scope():
    print("每个方法开始之前运行一次")
    msg = "测试function_scope"
    return msg


def test_function_scope_1(function_scope):
    assert function_scope == "测试function_scope"


def test_function_scope_2(function_scope):
    assert function_scope == "测试function_scope"



#运行结果
============================= test session starts =============================
platform win32 -- Python 3.7.3, pytest-5.1.2, py-1.8.0, pluggy-0.12.0 -- D:\program\Python37\python.exe
cachedir: .pytest_cache
rootdir: E:\virtual_workshop\pytest-demo\test_demo
collecting ... collected 2 items

test_function_scope.py::test_function_scope_1 每个方法开始之前运行一次
PASSED                     [ 50%]
test_function_scope.py::test_function_scope_2 每个方法开始之前运行一次
PASSED                     [100%]

============================== 2 passed in 0.03s ==============================

三. scope="class"

定义一个test_class_scope.py，写入如下代码并运行：

import pytest

@pytest.fixture(scope="class")
def class_scope():
    print("每个类开始之前运行一次")
    msg = "测试class_scope"
    return msg


class TestClassScope1():
    def test_class_scope_1(self, class_scope):
        assert class_scope == "测试class_scope"


class TestClassScope2():
    def test_class_scope_2(self, class_scope):
        assert class_scope == "测试class_scope"


#运行结果
============================= test session starts =============================
platform win32 -- Python 3.7.3, pytest-5.1.2, py-1.8.0, pluggy-0.12.0 -- D:\program\Python37\python.exe
cachedir: .pytest_cache
rootdir: E:\virtual_workshop\pytest-demo\test_demo
collecting ... collected 2 items

test_class_scope.py::TestClassScope1::test_class_scope_1 每个类开始之前运行一次
PASSED          [ 50%]
test_class_scope.py::TestClassScope2::test_class_scope_2 每个类开始之前运行一次
PASSED          [100%]

============================== 2 passed in 0.03s ==============================

四. scope="module"

定义一个test_module_scope.py，写入如下代码并运行：

import pytest

@pytest.fixture(scope="module")
def module_scope():
    print("每个模块开始之前运行一次")
    msg = "测试module_scope"
    return msg


class TestClassScope1():
    def test_module_scope_1(self, module_scope):
        assert module_scope == "测试module_scope"


class TestClassScope2():
    def test_module_scope_2(self, module_scope):
        assert module_scope == "测试module_scope"



#运行结果
============================= test session starts =============================
platform win32 -- Python 3.7.3, pytest-5.1.2, py-1.8.0, pluggy-0.12.0 -- D:\program\Python37\python.exe
cachedir: .pytest_cache
rootdir: E:\virtual_workshop\pytest-demo\test_demo2
collecting ... collected 2 items

test_module_scope.py::TestClassScope1::test_module_scope_1 每个模块开始之前运行一次
PASSED        [ 50%]
test_module_scope.py::TestClassScope2::test_module_scope_2 PASSED        [100%]

============================== 2 passed in 0.03s ==============================

五. scope="session"

在test_demo3包下定义一个conftest.py，代码如下：

import pytest

@pytest.fixture(scope="session")
def session_scope():
    print("一个session(多个模块)开始之前调用一次")
    msg = "一个session(多个模块)开始之前调用一次"
    return msg

然后定义两个模块，一个是test_session_scope1.py，一个是test_session_scope2.py

#test_session_scope1.py
def test_session_scope1(session_scope):
    assert session_scope == "测试session_scope"


#test_session_scope2.py
def test_session_scope2(session_scope):
    assert session_scope == "测试session_scope"


#运行结果
============================= test session starts =============================
platform win32 -- Python 3.7.3, pytest-5.1.2, py-1.8.0, pluggy-0.12.0 -- D:\program\Python37\python.exe
cachedir: .pytest_cache
rootdir: E:\virtual_workshop\pytest-demo\test_demo3
collecting ... collected 2 items

test_session_scope1.py::test_session_scope1 一个session(多个模块)开始之前运行一次
PASSED                       [ 50%]
test_session_scope2.py::test_session_scope2 PASSED                       [100%]

============================== 2 passed in 0.03s ==============================

六. 实例化顺序

session > module > class > function。一个比较好的例子是这篇博客中的：

import pytest

order = []

@pytest.fixture(scope="session")
def s1():
    order.append("s1")


@pytest.fixture(scope="module")
def m1():
    order.append("m1")


@pytest.fixture
def f1(f3, a1):
    # 先实例化f3, 再实例化a1, 最后实例化f1
    order.append("f1")
    assert f3 == 123


@pytest.fixture
def f3():
    order.append("f3")
    a = 123
    yield a


@pytest.fixture
def a1():
    order.append("a1")


@pytest.fixture
def f2():
    order.append("f2")


def test_order(f1, m1, f2, s1):
    # m1、s1在f1后，但因为scope范围大，所以会优先实例化
    assert order == ["s1", "m1", "f3", "a1", "f1", "f2"]