如何在没有文件系统访问权限的情况下对“mkdir"功能进行单元测试? [英] How to Unit Test 'mkdir' function without file system access?

问题描述

我使用 py.test 进行单元测试.我有这样的事情:

I use py.test for unit testing. I have something just like this:

Class Site(object):

    def set_path(self):
        """Checks if the blog folder exists. Creates new folder if necessary."""        
        if not os.path.isdir(self.user_dir):
            print "Creating new directory:", self.user_dir
            os.mkdir(self.user_dir)
        else:
            print "\n**", self.user, "directory already exists."

如何在不接触文件系统的情况下对其进行单元测试?

在处理此类问题时是否有一般的经验法则?

Is there a general rule of thumb when dealing with such problems?

想了很久，还是想不出解决办法.

I've thought about it for a long time, and I cannot think of a solution.

我的应用程序将包含许多文件系统访问，我不知道如何在单元测试时合并这些方法.

My application will contain many file system accesses, and I don't know how to incorporate those methods when unit testing.

我想专门测试一个文件夹是否在正确的路径中创建.路径是self.user_dir.

I want to specifically test that a folder is created in the correct path. The path is self.user_dir.

我还有一个下载功能，可以将图像下载到 self.user_dir.我想测试图像是否已下载.将如何进行测试?

I also have a download function, that downloads an image into self.user_dir. I want to test that the image is downloaded. How would one go about testing this?

推荐答案

您可以使用两种方法，模拟(首选)或隔离:

There are two approaches you could use, mocking (preferred) or isolation:

模拟:

在测试时，将 os.mkdir 替换为模拟"版本:

At test time, replace os.mkdir with a "mock" version:

class MockMkdir(object):
    def __init__(self):
        self.received_args = None
    def __call__(*args):
        self.received_args = args

class MyTest(unittest.TestCase):
    def setUp():
        self._orig_mkdir = os.mkdir
        os.mkdir = MockMkdir()
    def tearDown():
        os.mkdir = self._orig_mkdir
    def test_set_path(self):
        site = Site()
        site.set_path('foo/bar')
        self.assertEqual(os.mkdir.received_args[0], 'foo/bar')

Mock 是一个库，可帮助您以更少的代码行更优雅地完成此类事情.

Mock is a library that helps you do this kind of thing more elegantly and with fewer lines of code.

隔离

使用 chroot 在隔离的文件系统中运行单元测试.运行每个测试用例后，将文件系统恢复到干净状态.这是一种大锤的方法，但对于测试非常复杂的库，使用这种方法可能更容易.

Use chroot to run your unittests within an isolated filesystem. After running each test case, revert the filesystem to a clean state. This is something of a sledgehammer approach but for testing very complicated libraries it might be easier to get this approach to work.

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