Hack Bulgaria
github.com/HackBulgaria
Mocking
The problem
from datetime import datetime
def is_weekday():
today = datetime.today()
return 0 <= today.weekday() < 5
assert is_weekday()Monkey Patching
def is_weekday():
today = datetime.today()
return 0 <= today.weekday() < 5
datetime.today = lambda: datetime.datetime(year=2020, day=22, month=4)
assert is_weekday()Monkey patching is the replacement of one object with another at runtime.
Mocks
import datetime
from unittest.mock import Mock
friday = datetime.datetime(year=2020, month=4, day=24)
datetime = Mock()
def is_weekday():
today = datetime.datetime.today()
return (0 <= today.weekday() < 5)
datetime.datetime.today.return_value = friday
assert is_weekday()Recursion
A Mock must simulate any object that it replaces. To achieve such flexibility, it creates its attributes when you access them
json = Mock()
# <Mock id='140452118049488'>
json.dumps()
# <Mock name='mock.dumps()' id='140452118553488'>
json.dumps().get('student').id
# <Mock name='mock.dumps().get().id' id='140452116708560'>Methods & Properties
- my_mock.assert_called()
- my_mock.assert_called_once()
- my_mock.assert_called_with(*args, **kwargs)
- my_mock.assert_called_once_with(*args, **kwargs)
- my_mock.call_count
- my_mock.call_args_list
Managing Return values
import datetime
from unittest.mock import Mock
friday = datetime.datetime(year=2020, month=4, day=24)
saturday = datetime.datetime(year=2020, month=4, day=25)
datetime = Mock()
def is_weekday():
today = datetime.datetime.today()
return (0 <= today.weekday() < 5)
datetime.datetime.today.return_value = friday
assert is_weekday()
datetime.datetime.today.return_value = saturday
assert not is_weekday()
Managing Side effects
from requests.exceptions import Timeout
from unittest.mock import Mock
requests = Mock()
def get_cat_facts():
r = requests.get('https://cat-fact.herokuapp.com/facts')
if r.status_code == 200:
return r.json()
class TestGetCats(unittest.TestCase):
def test_get_cats_timeout(self):
requests.get.side_effect = Timeout
with self.assertRaises(Timeout):
get_cat_facts()patch()
as decorator
from unittest.mock import patch
from datetime import datetime
from calendar import is_weekday
class CalendarTests(unittest.TestCase):
@patch('calendar.datetime.datetime')
def test_sunday_is_not_weekday(self, datetime_mock):
datetime_mock.today.return_value = datetime(year=2020, month=4, day=26)
self.assertFalse(is_weekday())patch()
as context manager
from unittest.mock import patch
from datetime import datetime
from calendar import is_weekday
class CalendarTests(unittest.TestCase):
def test_is_weekday(self):
with patch('calendar.datetime.datetime') as datetime_mock:
sunday = datetime(year=2020, month=4, day=26)
datetime_mock.today.return_value = sunday
self.assertFalse(is_weekday())
with patch('calendar.datetime.datetime') as datetime_mock:
wednesday = datetime(year=2020, month=4, day=22)
datetime_mock.today.return_value = wednesday
self.assertTrue(is_weekday())Where to Patch?
Example
from datetime import datetime
my_datetime = datetime
def is_weekday():
today = my_datetime.today()
return (0 <= today.weekday() < 5)
Change the tests
import unittest
from unittest.mock import patch
from datetime import datetime
from calendar import is_weekday
class CalendarTests(unittest.TestCase):
@patch('calendar.datetime')
def test_sunday_is_not_weekday(self, datetime_mock):
sunday = datetime(year=2020, month=4, day=26)
datetime_mock.today.return_value = sunday
self.assertFalse(is_weekday())
if __name__ == '__main__':
unittest.main()AssertionError: True is not false
----------------------------------------------------------------------
Ran 1 test in 0.002s
FAILED (failures=1)Correct the tests
import unittest
from unittest.mock import patch
from datetime import datetime
from calendar import is_weekday
class CalendarTests(unittest.TestCase):
@patch('calendar.my_datetime')
def test_sunday_is_not_weekday(self, datetime_mock):
sunday = datetime(year=2020, month=4, day=26)
datetime_mock.today.return_value = sunday
self.assertFalse(is_weekday())
if __name__ == '__main__':
unittest.main()╰─Ѫ py mocks/test_calendar.py 1 ↵
.
----------------------------------------------------------------------
Ran 1 test in 0.002s
OK
- What does happen when you import something?!
- patch() temporarily changes the object that a name points to with another one
- patch() the object where it is looked up!!!
- https://docs.python.org/3/library/unittest.mock.html#where-to-patch
Mock problems
import unittest
from unittest.mock import patch
from datetime import datetime
from calendar import is_weekday
class CalendarTests(unittest.TestCase):
@patch('calendar.my_datetime')
def test_sunday_is_not_weekday(self, datetime_mock):
sunday = datetime(year=2020, month=4, day=26)
datetime_mock.tdoay.return_value = sunday
self.assertFalse(is_weekday())
if __name__ == '__main__':
unittest.main()TypeError: '<=' not supported between instances of 'int' and 'MagicMock'
----------------------------------------------------------------------
Ran 1 test in 0.004s
FAILED (errors=1)Mock specifications
import unittest
from unittest.mock import patch
from datetime import datetime
from calendar import is_weekday
class CalendarTests(unittest.TestCase):
@patch('calendar.my_datetime', spec=datetime) # or autospec=True
def test_sunday_is_not_weekday(self, datetime_mock):
sunday = datetime(year=2020, month=4, day=26)
datetime_mock.tdoay.return_value = sunday
self.assertFalse(is_weekday())
if __name__ == '__main__':
unittest.main()AttributeError: Mock object has no attribute 'tdoay'
----------------------------------------------------------------------
Ran 1 test in 0.015s
FAILED (errors=1)Python 101 9th Mocking
By Hack Bulgaria
