FreezeGun: Let your Python tests travel through time

FreezeGun is a library that allows your Python tests to travel through time by mocking the datetime module.

Usage

Once the decorator or context manager have been invoked, all calls to datetime.datetime.now(), datetime.datetime.utcnow(), datetime.date.today(), time.time(), time.localtime(), time.gmtime(), and time.strftime() will return the time that has been frozen.

Decorator

from freezegun import freeze_time
import datetime
import unittest


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

# Or a unittest TestCase - freezes for every test, from the start of setUpClass to the end of tearDownClass

@freeze_time("1955-11-12")
class MyTests(unittest.TestCase):
    def test_the_class(self):
        assert datetime.datetime.now() == datetime.datetime(1955, 11, 12)

# Or any other class - freezes around each callable (may not work in every case)

@freeze_time("2012-01-14")
class Tester(object):
    def test_the_class(self):
        assert datetime.datetime.now() == datetime.datetime(2012, 1, 14)

# Or method decorator, might also pass frozen time object as kwarg

class TestUnitTestMethodDecorator(unittest.TestCase):
    @freeze_time('2013-04-09')
    def test_method_decorator_works_on_unittest(self):
        self.assertEqual(datetime.date(2013, 4, 9), datetime.date.today())

    @freeze_time('2013-04-09', as_kwarg='frozen_time')
    def test_method_decorator_works_on_unittest(self, frozen_time):
        self.assertEqual(datetime.date(2013, 4, 9), datetime.date.today())
        self.assertEqual(datetime.date(2013, 4, 9), frozen_time.time_to_freeze.today())

    @freeze_time('2013-04-09', as_kwarg='hello')
    def test_method_decorator_works_on_unittest(self, **kwargs):
        self.assertEqual(datetime.date(2013, 4, 9), datetime.date.today())
        self.assertEqual(datetime.date(2013, 4, 9), kwargs.get('hello').time_to_freeze.today())

Context manager

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)

Raw use

from freezegun import freeze_time

freezer = freeze_time("2012-01-14 12:00:01")
freezer.start()
assert datetime.datetime.now() == datetime.datetime(2012, 1, 14, 12, 0, 1)
freezer.stop()

Timezones

from freezegun import freeze_time

@freeze_time("2012-01-14 03:21:34", tz_offset=-4)
def test():
    assert datetime.datetime.utcnow() == datetime.datetime(2012, 1, 14, 3, 21, 34)
    assert datetime.datetime.now() == datetime.datetime(2012, 1, 13, 23, 21, 34)

    # datetime.date.today() uses local time
    assert datetime.date.today() == datetime.date(2012, 1, 13)

@freeze_time("2012-01-14 03:21:34", tz_offset=-datetime.timedelta(hours=3, minutes=30))
def test_timedelta_offset():
    assert datetime.datetime.now() == datetime.datetime(2012, 1, 13, 23, 51, 34)

Nice inputs

FreezeGun uses dateutil behind the scenes so you can have nice-looking datetimes.

@freeze_time("Jan 14th, 2012")
def test_nice_datetime():
    assert datetime.datetime.now() == datetime.datetime(2012, 1, 14)

Function and generator objects

FreezeGun is able to handle function and generator objects.

def test_lambda():
    with freeze_time(lambda: datetime.datetime(2012, 1, 14)):
        assert datetime.datetime.now() == datetime.datetime(2012, 1, 14)

def test_generator():
    datetimes = (datetime.datetime(year, 1, 1) for year in range(2010, 2012))

    with freeze_time(datetimes):
        assert datetime.datetime.now() == datetime.datetime(2010, 1, 1)

    with freeze_time(datetimes):
        assert datetime.datetime.now() == datetime.datetime(2011, 1, 1)

    # The next call to freeze_time(datetimes) would raise a StopIteration exception.

tick argument

FreezeGun has an additional tick argument which will restart time at the given value, but then time will keep ticking. This is alternative to the default parameters which will keep time stopped.

@freeze_time("Jan 14th, 2020", tick=True)
def test_nice_datetime():
    assert datetime.datetime.now() > datetime.datetime(2020, 1, 14)

auto_tick_seconds argument

FreezeGun has an additional auto_tick_seconds argument which will autoincrement the value every time by the given amount from the start value. This is alternative to the default parameters which will keep time stopped. Note that given auto_tick_seconds the tick parameter will be ignored.

@freeze_time("Jan 14th, 2020", auto_tick_seconds=15)
def test_nice_datetime():
    first_time = datetime.datetime.now()
    auto_incremented_time = datetime.datetime.now()
    assert first_time + datetime.timedelta(seconds=15) == auto_incremented_time

Manual ticks

FreezeGun allows for the time to be manually forwarded as well.

def test_manual_increment():
    initial_datetime = datetime.datetime(year=1, month=7, day=12,
                                        hour=15, minute=6, second=3)
    with freeze_time(initial_datetime) as frozen_datetime:
        assert frozen_datetime() == initial_datetime

        frozen_datetime.tick()
        initial_datetime += datetime.timedelta(seconds=1)
        assert frozen_datetime() == initial_datetime

        frozen_datetime.tick(delta=datetime.timedelta(seconds=10))
        initial_datetime += datetime.timedelta(seconds=10)
        assert frozen_datetime() == initial_datetime

Moving time to specify datetime

FreezeGun allows moving time to specific dates.

def test_move_to():
    initial_datetime = datetime.datetime(year=1, month=7, day=12,
                                        hour=15, minute=6, second=3)

    other_datetime = datetime.datetime(year=2, month=8, day=13,
                                        hour=14, minute=5, second=0)
    with freeze_time(initial_datetime) as frozen_datetime:
        assert frozen_datetime() == initial_datetime

        frozen_datetime.move_to(other_datetime)
        assert frozen_datetime() == other_datetime

        frozen_datetime.move_to(initial_datetime)
        assert frozen_datetime() == initial_datetime


@freeze_time("2012-01-14", as_arg=True)
def test(frozen_time):
    assert datetime.datetime.now() == datetime.datetime(2012, 1, 14)
    frozen_time.move_to("2014-02-12")
    assert datetime.datetime.now() == datetime.datetime(2014, 2, 12)

Parameter for move_to can be any valid freeze_time date (string, date, datetime).

Default arguments

Note that FreezeGun will not modify default arguments. The following code will print the current date. See here for why.

from freezegun import freeze_time
import datetime as dt

def test(default=dt.date.today()):
    print(default)

with freeze_time('2000-1-1'):
    test()

Installation

To install FreezeGun, simply:

$ pip install freezegun

On Debian systems:

$ sudo apt-get install python-freezegun