如何在用于单元测试的类方法中模拟python的datetime.now()? [英] How to mock python's datetime.now() in a class method for unit testing?

问题描述

我正在尝试为具有以下方法的类编写测试:

I'm trying to write tests for a class that has methods like:

import datetime
import pytz

class MyClass:
    def get_now(self, timezone):
        return datetime.datetime.now(timezone)

    def do_many_things(self, tz_string='Europe/London'):
        tz = pytz.timezone(tz_string)
        localtime_now = self.get_now(tz)
        ...
        return things

我想测试它，为此，我需要确保datetime.datetime.now()调用返回可预测的结果.

I want to test it, and to do so I need to make sure that the datetime.datetime.now() call returns something predictable.

我一直在阅读许多在测试中使用模拟的示例，但是找不到与我需要的东西完全一样的东西，而且我无法确定如何在测试中使用它.

I've been reading lots of examples of using Mock in tests, but haven't found anything quite like what I need, and I can't work out how to use it in my tests.

我将get_now()方法分离出来，以防更容易模拟它，而不是datetime.datetime.now()，但是我仍然很困惑.关于如何使用Mock为此编写UnitTest的任何想法? (这一切都在Django中，fwiw；在这种情况下，我不确定是否会有所不同.)

I separated the get_now() method out in case it's easier to mock that, instead of datetime.datetime.now(), but I'm still stumped. Any thoughts on how to write UnitTests for this using Mock? (This is all in Django, fwiw; I'm not sure if this makes a difference in this case.)

推荐答案

您将创建一个函数，该函数返回特定的日期时间，该日期时间本地化为传入的时区:

You'd create a function that returns a specific datetime, localized to the timezone passed in:

import mock

def mocked_get_now(timezone):
    dt = datetime.datetime(2012, 1, 1, 10, 10, 10)
    return timezone.localize(dt)

@mock.patch('path.to.your.models.MyClass.get_now', side_effect=mocked_get_now)
def your_test(self, mock_obj):
    # Within this test, `MyClass.get_now()` is a mock that'll return a predictable
    # timezone-aware datetime object, set to 2012-01-01 10:10:10.

这样，您可以测试是否正确处理了所得的时区感知日期时间.其他地方的结果应该显示正确的时区，但是日期和时间可以预测.

That way you can test if the resulting timezone-aware datetime is correctly being handled; results elsewhere should show the correct timezone but will have a predictable date and time.

在模拟get_now时，可以将mocked_get_now函数用作副作用.每当代码调用get_now时，调用都会被mock，和 mocked_get_now记录下来，并且其返回值用作返回给get_now的调用者的值.

You use the mocked_get_now function as a side-effect when mocking get_now; whenever code calls get_now the call is recorded by mock, and mocked_get_now is called, and it's return value used as the value returned to the caller of get_now.

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