Mock - Mocking and Testing Library, An Introduction

This deck goes a little deeper into the mocking framework, "mock".

Transcript

1. Mock - Mocking and Testing Library An Introduction.
2. About me { “name”: “Burton Williams”, “title”: “Software Engineer Contractor”, “email” : “burton.williams@kariblabs.com”, “github” : “ikiini”, “origin_country”: “St Vincent and the Grenadines” }
3. Agenda • What is Mock? • Why use Mock? • Basics. • Useful features. – patch. – side_effect. • Other features.
4. Agenda • What is Mock? • Why use Mock? • Basics. • Useful features. – patch. – side_effect. • Other features.
5. What is Mock? “Mock is a library for testing in Python. It allows you to replace parts of your system under test with mock objects and make assertions about how they have been used”
6. Agenda • What is Mock? • Why use Mock? • Basics. • Useful features. – patch. – side_effect. • Other features.
7. Why use Mock? • No more writing stubs. • The ability to change behavior of an object in the context of a test without affecting other tests that use the same object. • Test flexibility • Its easy!!!
8. Agenda • What is Mock? • Why use Mock? • Basics. • Useful features. – patch. – side_effect. • Other features.
9. Basics - creation • As simple as import and instantiate. – >>> from mock import Mock – >>> my_mock_object = Mock()
10. Basics - usage • Add attributes with values. – >>> my_mock_object.attr_x = 3 • Treat it like a method and add a return value. – >>> my_mock_object.return_value = 42 – >>> my_mock_object() – ... 42 • Monkey patch a method on a class we're testing. (extending on example above) – >>> class RealDeal(object): – ... def a_func(): – ... return “a_func was called” – >>> real = RealDeal() – >>> real.a_func = my_mock_object – >>> real.a_func() – ... 42
11. Basics - usage • Built-in mock functions. – assert_called_once_with – assert_called_with – call_count – called
12. Agenda • What is Mock? • Why use Mock? • Basics. • Useful features. – patch. – side_effect. • Other features.
13. Useful features - patch • Good for mocking classes instantiated in your code under test. • Access the mock that replaces the class by using the mock's return value. You can configure the mocked class however you need to from here. • Can be used in with statements or as a decorator on a test case or test class. As a decorator it comes in 3 flavors: – @patch – @patch.object – @patch.dict
14. Useful features – patch examples • with statement: • >>> with patch('package.module.Class') as mock: • ... class_instance = mock.return_value • ... class_instance.y = 2 • ... class_instance.method.return_value = 42 • ... real = package.module.Class() • ... real.method() # will return 42
15. Useful features – patch examples • @patch: – >>> from package.module import Class – >>> class ClassUnderTest(object): – ... def some_method(): – ... my_class = Class() – ... return my_class.method() – >>> – >>> class MyTestCase(unittest.TestCase): – ... @patch('package.module.Class') – ... def myTest(self, mock_class): – ... class_instance = mock_class.return_value – ... class_instance.method.return_value = 42 – ... real = ClassUnderTest() – ... self.assertEqual(42, real.method())
16. Useful features – side_effect • Allows you to vary the return values of a mock object. • Example: – >>> mock = Mock(side_effect=[4, 5, 6]) – >>> mock() – 4 – >>> mock() – 5 – >>> mock() – 6
17. Useful features – side_effect • Example cont'd: >>> vals = {(1, 2): 1, (2, 3): 2} – >>> def side_effect(*args): – ... return vals[args] – ... – >>> mock = Mock(side_effect=side_effect) – >>> mock(1, 2) – 1 – >>> mock(2, 3) – 2
18. Agenda • What is Mock? • Why use Mock? • Basics. • Useful features. – patch. – side_effect. • Other features.
19. Other features • Method call tracking • Exception raising • MagicMock vs Mock. – Pretty much the same thing, except that MagicMock has magic functions already built onto the mock. • Create a mock from an existing class.
20. Mock Docs. http://www.voidspace.org.uk/python/mock/index.html
21. Thank you!