Patch __call__ of a function

Question

I need to patch current datetime in tests. I am using this solution:

def _utcnow():
    return datetime.datetime.utcnow()


def utcnow():
    \"\"\"A proxy w         


        

Answer 1

As commented on the question, since datetime.datetime is written in C, Mock can't replace attributes on the class (see Mocking datetime.today by Ned Batchelder). Instead you can use freezegun.

$ pip install freezegun

Here's an example:

import datetime

from freezegun import freeze_time

def my_now():
    return datetime.datetime.utcnow()


@freeze_time('2000-01-01 12:00:01')
def test_freezegun():
    assert my_now() == datetime.datetime(2000, 1, 1, 12, 00, 1)

As you mention, an alternative is to track each module importing datetime and patch them. This is in essence what freezegun does. It takes an object mocking datetime, iterates through sys.modules to find where datetime has been imported and replaces every instance. I guess it's arguable whether you can do this elegantly in one function.