How to mock/set system date in pytest?

@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)