一、猴子补丁简介

在有些场景下的测试可能需要修改全局配置或者系统变量等操作，而这些操作仅仅是为了做一些测试，不希望永久的修改，此时就需要使用猴子补丁了，猴子补丁，即monkeypatch，是一个fixture，它提供了以下方法：

monkeypatch.setattr(obj, name, value, raising=True)
monkeypatch.setattr("somemodule.obj.name", value, raising=True)
monkeypatch.delattr(obj, name, raising=True)
monkeypatch.setitem(mapping, name, value)
monkeypatch.delitem(obj, name, raising=True)
monkeypatch.setenv(name, value, prepend=None)
monkeypatch.delenv(name, raising=True)
monkeypatch.syspath_prepend(path)
monkeypatch.chdir(path)

当测试结束后或者fixture执行完成后，monkeypatch中做的所有修改都将恢复

二、通过猴子补丁临时修改函数功能

如下，可以通过猴子补丁修改Path的home属性，进而临时修改函数的功能，然后进行测试，这样测试结束后，Path的home属性并不会真的发生修改

执行结果如下，很明显，在test_home测试函数中，Path.home属性并没有发生修改

$ pytest -s -v
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0 -- D:\Python39\python.exe
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('D:\\src\\blog\\tests\\.hypothesis\\examples')
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 2 items

test_demo.py::test_getssh PASSED
test_demo.py::test_home C:\Users\hitre
PASSED

========================================================================== 2 passed in 0.13s ===========================================================================

三、通过猴子补丁取消测试函数中request的使用

在conftest.py中编写如下代码即可

四、通过猴子补丁对环境变量测测试

如下，假设get_os_user_lower函数为被测函数，用例中可以通过猴子补丁对变量进行临时设置或删除，这样可以保证测试用例的准确性，否则当环境变量被修改或者被删除后，用例的稳定性将会收到影响

test_demo.py代码如下：

 执行结果如下：

$ pytest -v
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0 -- D:\Python39\python.exe
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('D:\\src\\blog\\tests\\.hypothesis\\examples')
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 2 items

test_demo.py::test_upper_to_lower PASSED [ 50%]
test_demo.py::test_raise_exception PASSED [100%]

========================================================================== 2 passed in 0.13s ===========================================================================

上述代码可以通过fixture继续优化如下：

 执行结果如下：

$ pytest -v
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0 -- D:\Python39\python.exe
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('D:\\src\\blog\\tests\\.hypothesis\\examples')
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 2 items

test_demo.py::test_upper_to_lower PASSED [ 50%]
test_demo.py::test_raise_exception PASSED [100%]

========================================================================== 2 passed in 0.13s ===========================================================================

五、通过猴子补丁对字典数据模拟测试

test_demo.py代码如下，其中DEFAULT_CONFIG为被测字典，create_connection_string为被测函数，测试当被测字典被修改或者被删除时的情况

 执行结果如下：

$ pytest -v
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0 -- D:\Python39\python.exe
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('D:\\src\\blog\\tests\\.hypothesis\\examples')
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 2 items

test_demo.py::test_connection PASSED [ 50%]
test_demo.py::test_missing_user PASSED [100%]

========================================================================== 2 passed in 0.13s ===========================================================================

上述代码可以通过fixture进行优化，如下：

 执行结果如下：

$ pytest -v
========================================================================= test session starts ==========================================================================
platform win32 -- Python 3.9.7, pytest-6.2.5, py-1.10.0, pluggy-1.0.0 -- D:\Python39\python.exe
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('D:\\src\\blog\\tests\\.hypothesis\\examples')
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 2 items

test_demo.py::test_connection PASSED [ 50%]
test_demo.py::test_missing_user PASSED [100%]

========================================================================== 2 passed in 0.12s ===========================================================================