test.py

import datetime

from freezegun import freeze_time
import pytest


def my_func(date=datetime.date.today()):
    is_monday = date.weekday() == 0
    return date, is_monday


@pytest.mark.parametrize("date,expected", [
    (datetime.date(2017, 7, 10), True),
    (datetime.date(2017, 10, 22), False),
])
def test_monday(date, expected):
    _, is_monday = my_func(date)
    assert is_monday is expected


@pytest.mark.parametrize("date,expected", [
    ('2017-07-10', True),
    ('2017-10-22', False),
])
def test_default(date, expected):
    with freeze_time(date):
        _, is_monday = my_func()
        assert is_monday is expected