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
I want to test it, and to do so I need to make sure that the
datetime.datetime.now() call returns something predictable.
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.
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.)
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
mocked_get_now is called, and it's return value used as the value returned to the caller of
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.