Testing with unittest.mock

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Testing with unittest.mock Ana Hristova

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♥ Every tester has the heart of a developer

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Crowd Investment Platform CONNECTING INVESTORS AND ENTREPRENEURS THROUGH FUNDING ana@fundedbyme.com

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No content

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Sweden

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unittest.mock Testing library

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Part of the Python Standard Library as of Python 3.3 unittest.mock

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For older versions: unittest.mock $ pip install mock

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unittest.mock helps you create mock objects and make assertions about them

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How is this helpful?

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You want to test code that depends on the " date or time

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You are building a shiny new app … # $ % % % % % & ' ( )

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Please wait… … while your tests are running *

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Mock MagicMock patch( )

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Mock objects Callable

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Mock objects Create attributes on demand

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Mock objects Record how you use the attributes

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Allow you to set return values or limit the available attributes Mock objects

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Examples

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>>> class Comment: ... ... def create(self, text, parent=None): ... pass ... comment = Comment()

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>>> comment.create = Mock(return_value=True) >>> comment.create(text=‘hello') True >>> comment.create. \ ... assert_called_once_with(text=‘hello’) >>> comment.create.called True >>> comment.create.call_args call(text='hello') >>> comment.call_count 1

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>>> mock = Mock() >>> mock >>> mock.method >>> mock.assetr_called_with(keyword=None)

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... AttributeError: Mock object has no attribute 'remove' >>> comment.remove >>> from unittest.mock import create_autospec >>> >>> comment = create_autospec(Comment)

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side effects

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>>> comment.create.side_effect = \ ... ConnectionError(“Connection refused”) >>> ... ConnectionError: Connection refused >>> comment.create.mock_calls [call(parent=None, text='Hello')] >>> >>> comment.create(text="Hello", parent=None)

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magic methods Mocking

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>>> mock = Mock() >>> mock.__len__ = Mock() >>> mock.__len__.return_value = 42 >>> len(mock) 42 ! !

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MagicMock with default implementations of magic methods Subclass of Mock

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>>> mock = MagicMock() >>> int(mock) 1 >>> len(mock) 0 >>> list(mock) [] >>> mock.__int__.called True

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patch( ) Used to patch objects within the scope of the test

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#event.py from datetime import date ! class Event(): ! def get_state(self): if self.end_date < date.today(): return "PAST" if self.start_date > date.today(): return "FUTURE" if self.start_date <= date.today() <= self.end_date: return "CURRENT"

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#test.py from datetime import date ! class EventTests(TestCase): def setUp(self): self.pycon = Event() self.pycon.start_date = date(2014, 5, 20) self.pycon.end_date = date(2014, 5, 21) ! @patch('event.date') def test_event_has_passed(self, mock_date): mock_date.today.return_value = date(2014, 5, 22) assert self.pycon.get_state() == "PAST"

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@patch('event.date') def test_event_has_passed(self, mock_date): mock_date.today.return_value = date(2014, 5, 22) assert self.pycon.get_state() == "PAST"

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class UserProfileSaveTests(TestCase): ! def setUp(self): self.profile = UserProfileFactory.build(user=UserFactory()) ! ! @patch("notifications.tasks.subscribe_to_newsletter.delay") def test_subscribe_to_newsletter(self, subscribe_mock): self.profile.newsletter = True self.profile.save() subscribe_mock.assert_called_once_with(self.profile.user)