使用 pytest 測試 __init__.py 中可選依賴項的導入：Python 3.5 /3.6 的行為不同

Question

我有一個用於 python 3.5 和 3.6 的包，它具有可選的依賴項，我想要在任一版本上運行的測試 (pytest)。

我在下面做了一個包含兩個文件的簡化示例，一個簡單的__init__.py ，其中導入了可選包“requests”（只是一個示例），並設置了一個標志來指示請求的可用性。

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

__init__.py文件內容：

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

requests_available = True

try:
    import requests
except ImportError:
    requests_available = False

test_init.py文件內容：

#!/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測試適用於 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 ===========================

但不是在 Python 3.5.4 上：

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 =======================================================

我有兩個問題：

1. 為什么我會看到這種差異？ 相關軟件包在 3.5 和 3.6 上的版本似乎相同。

2. 有沒有更好的方法來做我想做的事？ 我現在的代碼是從網上找到的例子拼接在一起的。 我試圖修補導入機制以避免“重新加載”，但我沒有成功。

Answer 1

我要么模擬__import__函數（在import modname語句后面調用的那個），要么通過添加自定義元路徑查找器來自定義導入機制。 例子：

改變sys.meta_path

添加一個自定義MetaPathFinder實現，該實現在嘗試導入pkgnames任何包時引發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

夾具no_requests將在調用時更改sys.meta_path ，因此自定義元路徑查找器從可以導入的包中過濾掉requests包名稱（我們不能在任何導入時引發，否則pytest本身會中斷）。 cleanup_imports只是為了確保在每次測試中都會重新導入mypackage 。

__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

在這里，fixture no_requests負責用一個會在import requests嘗試時引發的函數替換__import__函數，在其余的導入上做得很好。

Answer 2

import sys
from unittest.mock import patch

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

上面的代碼所做的是，它模擬了包optional_dependency沒有安裝並在上下文管理器( with ) 內的隔離環境中運行您的測試。

請記住，您可能需要根據您的用例重新加載被測module

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

Answer 3

如果測試測試可選功能，則在缺少該功能時應跳過它而不是通過測試。

test.support.import_module()是 Python 自動測試套件中用於在模塊丟失時跳過測試或測試文件的函數：

import test.support
import unittest

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

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

然后，在運行時：

> 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 ==========================