使用 pytest 在 init.py 中测试可选依赖项的导入：Python 3.5 /3.6 行为不同

Question

我有一个适用于 python 3.5 和 3.6 的包，它具有可选的依赖项，我希望在任一版本上进行运行测试 (pytest)。

我在下面做了一个由两个文件组成的简化示例，一个简单的 __init__.py，其中导入了可选包 "requests"（只是一个示例），并设置了一个标志以指示请求的可用性.

mypackage/
├── mypackage
│   └── __init__.py
└── test_init.py

__init__.py文件内容：

#!/usr/bin/env python
# -*- coding: utf-8 -*-

requests_available = True

try:
    import requests
except ImportError:
    requests_available = False

test_init.py文件内容：

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import pytest, sys

def test_requests_missing(monkeypatch):
    import mypackage
    import copy
    fakesysmodules = copy.copy(sys.modules)
    fakesysmodules["requests"] = None
    monkeypatch.delitem(sys.modules,"requests")
    monkeypatch.setattr("sys.modules", fakesysmodules)
    from importlib import reload
    reload(mypackage)
    assert mypackage.requests_available == False


if __name__ == '__main__':
    pytest.main([__file__, "-vv", "-s"])

test_requests_missing 测试适用于 Python 3.6.5:

runfile('/home/bjorn/python_packages/mypackage/test_init.py', wdir='/home/bjorn/python_packages/mypackage')
============================= test session starts ==============================
platform linux -- Python 3.6.5, pytest-3.6.1, py-1.5.2, pluggy-0.6.0 -- /home/bjorn/anaconda3/envs/bjorn36/bin/python
cachedir: .pytest_cache
rootdir: /home/bjorn/python_packages/mypackage, inifile:
plugins: requests-mock-1.5.0, mock-1.10.0, cov-2.5.1, nbval-0.9.0, hypothesis-3.38.5
collecting ... collected 1 item

test_init.py::test_requests_missing PASSED

=========================== 1 passed in 0.02 seconds ===========================

但不在 Python 3.5.4:

runfile('/home/bjorn/python_packages/mypackage/test_init.py', wdir='/home/bjorn/python_packages/mypackage')
========================================================= test session starts ==========================================================
platform linux -- Python 3.5.4, pytest-3.6.1, py-1.5.2, pluggy-0.6.0 -- /home/bjorn/anaconda3/envs/bjorn35/bin/python
cachedir: .pytest_cache
rootdir: /home/bjorn/python_packages/mypackage, inifile:
plugins: requests-mock-1.5.0, mock-1.10.0, cov-2.5.1, nbval-0.9.1, hypothesis-3.38.5
collecting ... collected 1 item

test_init.py::test_requests_missing FAILED

=============================================================== FAILURES ===============================================================
________________________________________________________ test_requests_missing _________________________________________________________

monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7f9a2953acc0>

    def test_requests_missing(monkeypatch):
        import mypackage
        import copy
        fakesysmodules = copy.copy(sys.modules)
        fakesysmodules["requests"] = None
        monkeypatch.delitem(sys.modules,"requests")
        monkeypatch.setattr("sys.modules", fakesysmodules)
        from importlib import reload
>       reload(mypackage)

test_init.py:13: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../anaconda3/envs/bjorn35/lib/python3.5/importlib/__init__.py:166: in reload
    _bootstrap._exec(spec, module)
<frozen importlib._bootstrap>:626: in _exec
    ???
<frozen importlib._bootstrap_external>:697: in exec_module
    ???
<frozen importlib._bootstrap>:222: in _call_with_frames_removed
    ???
mypackage/__init__.py:8: in <module>
    import requests
../../anaconda3/envs/bjorn35/lib/python3.5/site-packages/requests/__init__.py:97: in <module>
    from . import utils

.... VERY LONG OUTPUT ....

    from . import utils
../../anaconda3/envs/bjorn35/lib/python3.5/site-packages/requests/__init__.py:97: in <module>
    from . import utils
<frozen importlib._bootstrap>:968: in _find_and_load
    ???
<frozen importlib._bootstrap>:953: in _find_and_load_unlocked
    ???
<frozen importlib._bootstrap>:896: in _find_spec
    ???
<frozen importlib._bootstrap_external>:1171: in find_spec
    ???
<frozen importlib._bootstrap_external>:1145: in _get_spec
    ???
<frozen importlib._bootstrap_external>:1273: in find_spec
    ???
<frozen importlib._bootstrap_external>:1245: in _get_spec
    ???
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

name = 'requests', location = '/home/bjorn/anaconda3/envs/bjorn35/lib/python3.5/site-packages/requests/__init__.py'

>   ???
E   RecursionError: maximum recursion depth exceeded

<frozen importlib._bootstrap_external>:575: RecursionError
======================================================= 1 failed in 2.01 seconds =======================================================

我有两个问题：

为什么我会看到这种差异？相关包在 3.5 和 3.6 上似乎是相同的版本。
有没有更好的方法来做我想做的事？我现在拥有的代码是从网上找到的示例拼接在一起的。我试图修补导入机制以试图避免"reload"，但我没有成功。

Answer 1

如果测试测试可选功能，如果缺少该功能，则应跳过而不是通过。

test.support.import_module() 是 Python 自动测试套件中使用的函数，用于在缺少模块时跳过测试或测试文件：

import test.support
import unittest

nonexistent = test.support.import_module("nonexistent")

class TestDummy(unittest.testCase):
    def test_dummy():
        self.assertTrue(nonexistent.vaporware())

然后，当运行:

> python -m py.test -rs t.py

<...>
collected 0 items / 1 skipped

=========================== short test summary info ===========================
SKIP [1] C:\Python27\lib\test\support\__init__.py:90: SkipTest: No module named
nonexistent
========================== 1 skipped in 0.05 seconds ==========================

Answer 2

我要么模拟 __import__ function（在 import modname 语句后面调用的那个），要么通过添加自定义元路径查找器来自定义导入机制。示例：

改变`sys.meta_path`

添加自定义 MetaPathFinder 实现，在尝试导入 pkgnames 中的任何包时引发 ImportError：

class PackageDiscarder:
    def __init__(self):
        self.pkgnames = []
    def find_spec(self, fullname, path, target=None):
        if fullname in self.pkgnames:
            raise ImportError()


@pytest.fixture
def no_requests():
    sys.modules.pop('requests', None)
    d = PackageDiscarder()
    d.pkgnames.append('requests')
    sys.meta_path.insert(0, d)
    yield
    sys.meta_path.remove(d)


@pytest.fixture(autouse=True)
def cleanup_imports():
    yield
    sys.modules.pop('mypackage', None)


def test_requests_available():
    import mypackage
    assert mypackage.requests_available


@pytest.mark.usefixtures('no_requests2')
def test_requests_missing():
    import mypackage
    assert not mypackage.requests_available

fixture no_requests 将在调用时更改 sys.meta_path，因此自定义元路径查找器从可以导入的包名称中过滤掉 requests 包名称（我们不能raise 任何导入或 pytest 本身都会中断）。 cleanup_imports只是为了确保每次测试都会重新导入mypackage。

嘲笑`import`

import builtins
import sys
import pytest


@pytest.fixture
def no_requests(monkeypatch):
    import_orig = builtins.__import__
    def mocked_import(name, globals, locals, fromlist, level):
        if name == 'requests':
            raise ImportError()
        return import_orig(name, locals, fromlist, level)
    monkeypatch.setattr(builtins, '__import__', mocked_import)


@pytest.fixture(autouse=True)
def cleanup_imports():
    yield
    sys.modules.pop('mypackage', None)


def test_requests_available():
    import mypackage
    assert mypackage.requests_available


@pytest.mark.usefixtures('no_requests')
def test_requests_missing():
    import mypackage
    assert not mypackage.requests_available

在这里，fixture no_requests 负责将 __import__ 函数替换为将在 import requests 尝试时引发的函数，在其余导入中表现良好。

Answer 3

import sys
from unittest.mock import patch

def test_without_dependency(self):
    with patch.dict(sys.modules, {'optional_dependency': None}):
        # do whatever you want

上面的代码所做的是，它模拟未安装包 optional_dependency 并在 context-manager(with).[=15= 中的隔离环境中运行测试。 ]

请记住，根据您的用例，您可能需要重新加载 module 正在测试的

import sys
from unittest.mock import patch
from importlib import reload

def test_without_dependency(self):
    with patch.dict(sys.modules, {'optional_dependency': None}):
        reload(sys.modules['my_module_under_test'])
        # do whatever you want

使用 pytest 在 init.py 中测试可选依赖项的导入：Python 3.5 /3.6 行为不同

Test for import of optional dependencies in init.py with pytest: Python 3.5 /3.6 differs in behaviour

python

pytest

python-3.5

python-3.6

改变`sys.meta_path`

嘲笑`import`

使用 pytest 在 __init__.py 中测试可选依赖项的导入：Python 3.5 /3.6 行为不同

Test for import of optional dependencies in __init__.py with pytest: Python 3.5 /3.6 differs in behaviour

python

pytest

python-3.5

python-3.6

改变sys.meta_path

嘲笑__import__

使用 pytest 在 init.py 中测试可选依赖项的导入：Python 3.5 /3.6 行为不同

Test for import of optional dependencies in init.py with pytest: Python 3.5 /3.6 differs in behaviour

改变`sys.meta_path`

嘲笑`import`