Unit Tests and Mocks: Testing in Python

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1. Unit Tests and Mocks Testing in Python
2. What is a Unit Test? • Test individual software units • By devs for devs • Is my code doing things right?
3. Good Unit Tests • Thorough • Fast • Stable • Few The Magic Tricks of Testing by Sandi Metz (http://bit.ly/2rLW5w8)
4. import unittest class MyTest(unittest.TestCase): def test_isupper(self): self.assertTrue(‘foo’.isupper()) if __name__ == ‘__main__’: unittest.main()
5. Unit Test Tools • Test Case • Test Fixture • Test Suite
6. Test Case • Grouping related tests • Describe independent testing scenario
7. class MyTest(unittest.TestCase): def test_isupper(self): self.assertTrue(‘foo’.isupper()) def test_upper(self): self.assertEqual(‘foo’.upper(), ‘FOO’)
8. Test Fixture • Common setup and cleanup code • Run automatically for each test
9. class MyTest(unittest.TestClass): def SetUp(self): self.common_resource = Resource() def TearDown(self): self.common_resource.dispose() def test_use_resource(self): # use common resource...
10. Assert Methods
11. assertRaises method def test_file_not_found(self): with self.assertRaises(FileNotFoundError): read_file_function(“missing_file.txt”)
12. Extras @unittest.skip(“skip this test”) def test_skip(self): self.fail(“should not run”) @unittest.expectFailure def test_fail(self): self.assertEqual(1, 0, “known broken test”)
13. Mocks • Object double • Mocks aren’t stubs! • Mocks use behavior verification • Mocks have expectations Mocks Aren't Stubs by Martin Fowler (http://bit.ly/2luLoeC)
14. Why mock? • Avoid integration testing • Avoid system calls • Avoid using expensive resources • Avoid network requests
15. unittest.mock class • unittest mocking base class • Simplest mocking implementation • Requires manual setup for doubled object attributes and methods
16. unittest.MagicMock class • Mock subclass • Default magic method implementations • More capable than Mock
17. from unittest.mock import MagicMock car = Car() car.get_make = MagicMock(return_value=”Honda”) car.get_make() car.get_make.assert_called()
18. Mock spec • Mock from object attributes and methods ◦ dir(object) • Object spec from dir(object) • Can generate automatically ◦ Prevent API drift
19. Mock autospec from unittest.mock import create_autospec mock_function = create_autospec(get_car_make, return_value=”Honda”) mock_function() # returns “Honda” mock_function.assert_called_once()
20. Mock autospec from unittest.mock import create_autospec def my_function(a, b): pass mock_function = create_autospec(my_function, return_value=None) mock_function(1, 2) mock_function.assert_called_once_with(1, 2)
21. Patch decorator from unittest.mock import patch ... @patch(“myapp.Car.get_make”, autospec=True) def test_method(self, mock_function): myapp.Car.get_make() mock_function.assert_called()
22. Patch decorator @patch(“myapp.Car”) def test_method(self, MockCar): myapp.Car() assert MockCar is myapp.Car assert MockCar.called
23. Mock Side Effects @patch(“myapp.Driver.licensed”) def test_method(self, mock_function): mock_function.side_effect = Exception(“Driver not licensed”) myapp.Car.drive()
24. Successful Mocking • Keep in sync with API • Keep mocks simple • Generate specs automatically
25. Beyond Basic Mocks • httmock ◦ HTTP requests • localstack ◦ AWS services
26. Useful Links • The Magic Tricks of Testing by Sandi Metz (http://bit.ly/2rLW5w8) • Mocks Aren't Stubs by Martin Fowler (http://bit.ly/2luLoeC) • Simple Smalltalk Testing: With Patterns by Kent Beck (http://bit.ly/2sEYA1F) • Python Mocks: A Gentle Introduction by Leonardo Giodani (http://bit.ly/2rCHeE5)