How to mock/set system date in pytest?

Question

In some of my tests I am having a problem that they fail on Travis because of time and time zone problems, so I want to mock system time for my test. How can I do this?

Answer 1

AFAIK, you can't mock builtin methods.

One approach I have often done is to change my code a bit to not use datetime directly to obtain the date, but a wrapper function somewhere:

# mymodule.py

def get_today():
   return datetime.date.today()

This makes it trivial to just mock it in your test:

def test_something():
    with mock.patch('mymodule.get_today', return_value=datetime.date(2014, 6, 2)):
        ...

You can also use the freezegun module.

Answer 2

@Brian-Kruger's answer is the best one. I've voted to undelete it. In the meantime...

Use freezegun (repo).

From the README:

from freezegun import freeze_time

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