如何模拟 Python 类以在每次实例化类时返回唯一的自动规范模拟实例?

Question

我正在编写一个创建subprocess.Popen管道的程序。我试图模拟subprocess.Popen以便每个调用返回一个不同的MagicMock这样我就可以确保在管道中的特定(或所有(进程上调用方法。

我也希望这个模拟是基于subprocess.Popen自动规范的，但不断收到一个错误，我无法基于模拟自动规范。

目前我的代码如下：

@pytest.fixture
def Popen(mocker: 'pytest_mock.MockFixture'):
def popen_factory(*args, **kwargs):
popen = mocker.MagicMock()  # mocker.create_autospec(subprocess.Popen)
popen.stdin = open(os.devnull, "wb")
popen.stdout = open(os.devnull, "rb")
popen.wait.return_value = 0
return popen
Popen = mocker.patch.object(subprocess, 'Popen', autospec=True)
Popen.side_effect = popen_factory
yield Popen

Answer 1

由于mocker.patch.object(subprocess, 'Popen', autospec=True)覆盖了subprocess.Popen，我必须将现有值分配给局部变量，并改用它。

@pytest.fixture
def Popen(mocker: 'pytest_mock.MockFixture'):
real_Popen = subprocess.Popen
def popen_factory(*args, **kwargs):
popen = mocker.create_autospec(real_Popen)
popen.stdin = open(os.devnull, "wb")
popen.stdout = open(os.devnull, "rb")
popen.wait.return_value = 0
return popen
Popen = mocker.patch.object(subprocess, 'Popen', autospec=True)
Popen.side_effect = popen_factory
yield Popen