python单元测试中的模拟常量不起作用 [英] Mock constant in python unit test doesn't work

问题描述

我试图在我的 python 单元测试中模拟一个常量.

I'm trying to mock a constant in my python unit test.

我有一个名为 settings.py 的模块，它包含一组常量，特别是我有这个:

I've a module called settings.py which contains a set of constants, in particular I've this one:

REL_PATH = "my/path/{}/file.csv"

然后在另一个模块中我有这个函数，它使用 REL_PATH 变量，如下所示:

Then in another module I've this function which use REL_PATH variable like this:

from path.for.REL_PATH.setting import REL_PATH

def create_csv(missing_path_here):
    columns = ["col_a", "col_b", ...]
    empty_df = pd.DataFrame(columns=columns)
    Writer(empty_df, REL_PATH.format(missing_path_here)).write_csv()

在我的单元测试中，我有以下代码:

In my unit test I've the following code:

class TestCreateAnomaliesRepositoryCsv(unittest.TestCase):

    @patch("path.for.setting.REL_PATH", "another/custom/path/file.csv")
    def test_create_anomalies_repository_csv(self):
         create_csv(missing_path_here="test")

我希望通过这种方式将在another/custom/path/"路径下创建 csv 文件，但仍然在原始目录中创建 csv 文件.

I expect that in this way the csv file will be created under "another/custom/path/" path, but still the csv file is created in the original directory.

我也试过这样做:

def test_create_anomalies_repository_csv(self):
    with path("path.for.setting.REL_PATH", "another/custom/path/file.csv")
        create_csv(missing_path_here="test")

但最终结果是一样的.

我做错了什么?

推荐答案

如果修补一个对象，您必须始终修补模块中使用的对象，例如如果你在你的模块 module 中以 from x import y 的形式导入它，你必须修补 module.y 而不是 xy.这在 文档 中有描述，并且有一个很好的Ned Batchelder 的博文更详细地描述了该问题.在您的情况下，您需要:

If patching an object, you have to always patch the object as used in the module, e.g. if you have imported it in the form: from x import y in your module module, you have to patch module.y instead of x.y. This is described in the documentation, and there is a nice blog post by Ned Batchelder describing the problem in more detail. In your case you need:

@patch("path.to.using_module.REL_PATH", "another/custom/path/file.csv")
def test_create_anomalies_repository_csv(self):
     create_csv(missing_path_here="test")

前提是 path.to.using_module.py 像这样导入常量:

provided that path.to.using_module.py imports the constant like this:

from path.for.setting import REL_PATH

您尝试的另一个变体是等效的，也可以使用:

The other variant you tried is equivalent and will also work:

def test_create_anomalies_repository_csv(self):
    with path("path.to.using_module.REL_PATH", "another/custom/path/file.csv")
        create_csv(missing_path_here="test")

总而言之，您必须始终检查要使用的对象是如何导入的.基本上有两种情况:

To summarize, you always have to check how the object to use is imported. There are basically two cases:

• 对象在 sut.py 中导入，如 import module 或 import module.object - 在这种情况下，它可以被修补为 <代码>module.object
• 对象在 sut.py 中导入，就像 from module import object - 在这种情况下 sut.py 使用本地引用来引用到对象，并对 sut.object
进行修补

• the object is imported in sut.py like import module or import module.object - in this case it can be patched as module.object
• the object is imported in sut.py like from module import object - in this case sut.py uses a local reference to refer to the object, and the patching shall be done for sut.object

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