How to mock python's datetime.now() in a class method for unit testing?

Question

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 dat         


        

Answer 1

If you don't want to install anything this is the simplest way. Simply use, Mock class -

class NewDt(datetime.date):
    @classmethod
     def now(cls):
           return datetime.datetime.strptime('2020-07-10 05:20:20', '%Y-%m-%d %H:%M:%S')

And use this patch before mock function

 @mock.patch('module path', NewDt)

Answer 2

I'm using date, but the same idea should work for datetime:

class SpoofDate(date):
    def __new__(cls, *args, **kwargs):
        return date.__new__(date, *args, **kwargs)

...

from mock import patch

@patch('some.module.date', SpoofDate)
def testSomething(self):
    SpoofDate.today = classmethod(lambda cls : date(2012, 9, 24))

Where some.module imports date. Patch is replacing the imported date with SpoofDate, which you can then redefine to do whatever you want.

Answer 3

Having asked this question originally...

As @Jocelyn delalande suggested, I've been happily using freezegun for years now.

Another option is python-libfaketime, which can be much faster than freezegun, but doesn't work on Windows and sounds a bit fiddly.

A newer option is time-machine, introduced in this blog post that compares the three options.

Answer 4

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.

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.

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.

Answer 5

Using patch of unittest.mock

from unittest.mock import patch

@patch('MyClass.datetime')
def test_foo(self, mock_datetime):
    mock_datetime.datetime.now.return_value = datetime.datetime(2019, 5, 7) #SOME_MOCKED_DATE

Note that we're overriding datetime module that is imported only in our class

The class for which we are writing the test:

import datetime

class MyClass:
    def foo():
       localtime_now = datetime.datetime.now(timezone)

We need not have to separate it as get_now() method just to make it easier to mock.

Answer 6

You could use freezegun :

from freezegun import freeze_time

def test():
    assert datetime.datetime.now() != datetime.datetime(2012, 1, 14)
    with freeze_time("2012-01-14"):
        assert datetime.datetime.now() == datetime.datetime(2012, 1, 14)
    assert datetime.datetime.now() != datetime.datetime(2012, 1, 14)

It basically mocks datetime module calls.