Entertaining testing with pytest

What seems wrong with python unittest and why pytest can serve as an alternative. Pytest fixtures, parameterizing, tips and tricks, etc.

Transcript

1. Entertaining testing with pytest Roman Imankulov / @rdotpy / 21 Apr 2017
2. Why developers don’t like writing tests?
3. Testing in Python is a religion • Original sin • Absolution through pain and suffering • Mystical experience
4. Original sin • Original sin — dynamic typing and duck typing • As a result, a natural inclination of a Python developer to create little and stupid mistakes exposed as runtime errors
5. Absolution through pain and suffering Boilerplate Code class TestSequenceFunctions(unittest.TestCase): def setUp(self): ... def tearDown(self): ... def testFoo(self): ...
6. Absolution through pain and suffering Verbose asserts self.assertEqual(foo, 1, 'foo is not equal to one')
7. Mystical experience Django testing setups & teardowns
8. Are there any alternatives?
9. pytest
10. file: test_something.py def test_lowercase(): name = "OPOPython" assert name.lower() == "opopython"
14. pytest is not a yet another xUnit framework!
15. pytest fixtures That’s what makes the difference
16. pytest fixtures Naive approach. How I’d do it myself file: fixtures.py def get_user(): return User(name='Roman', age=33, ...) file: test_user.py def test_user(): user = get_user() assert user.name == 'Roman'
17. pytest fixtures Pytest approach file: conftest.py @pytest.fixture def user(): return User(name='Roman', age=33, ...) file: test_user.py def test_user(user): assert user.name == 'Roman'
18. Fixture dependencies
19. @pytest.fixture def user(): return User(name='Roman', age=33, ...) @pytest.fixture def task(user): return Task(user=user, content='...') def test_task(task): assert task.user.name == 'Roman'
20. Fixture dependencies. Patching object @pytest.fixture def premium(user) user.set_premium() def test_premium(user, premium): assert user.is_premum()
21. yield_fixture 2 in 1, setup and teardown
22. @pytest.yield_fixture def user(): obj = User(name='Roman', age=30, ...) yield obj obj.delete()
23. Fixture scopes • function scope • module scope • session scope
24. Session fixture. Local cache @pytest.yield_fixture(scope='session', autouse=True) def local_cache(): old_settings = settings.CACHES settings.CACHES = {'default': {…}} yield settings.CACHES = old_settings
25. Function fixture. Database transaction rollback @pytest.yield_fixture def tx(): db().start_transaction() yield db().rollback() def test_user(user, tx, project, task): # project & task will be removed automatically
26. Session fixture. Clean redis @pytest.yield_fixture(scope='session') def redis_server(): proc = subp.Popen(['redis-server', '--port', 7777], ... ) yield proc proc.terminate() @pytest.fixture def rc(redis_server): client = redis.StrictRedis('redis://127.0.0.1:7777') client.flushall() return client
27. fixtures parametrization
28. Function returning a function @pytest.fixture def set_lang(user): def func(lang_code): user.set_lang(lang_code) return func def test_languages(user, set_lang): set_lang('pt') ...
29. Crazy things
30. Fixtures in a separate thread http://bit.ly/test_pool @pytest.fixture(scope='session') def item_gen(): gen = Generator(lambda: .) gen.start() return gen @pytest.yield_fixture def item(item_gen, item_rel): item = item_gen.get() yield item item_rel.put(item) @pytest.fixture(scope='session') def item_rel(): rel = Releaser(lambda o: ...) rel.start() return rel
31. More use cases for fixtures • warnings: turn MySQL warnings to errors • mock: initialize mockup objects • freezegun: time management • selenium: run a web driver
32. What else @pytest.mark.parametrize("input,expected", [ ("3+5", 8), ("2+4", 6), ]) def test_eval(input, expected): assert eval(input) == expected
33. What else def pytest_addoption(parser): parser.addoption("--clean-mysql", action="store_true", default=False) @pytest.fixture(scope='session', autouse=True) def clean_mysql(request): if not request.config.getoption(‘--clean-mysql'): return # clean MySQL tables heres
34. What else • pytest-sugar: beautiful output • pytest-django: integration with Django • pytest-xdist: parallel and distributed testing
35. What else • tox: testing against different versions of Python • detox: the same, but in parallel [tox] envlist = py27,py35,py36 [testenv] deps=pytest commands=py.test
36. Thank you! Questions? Roman Imankulov / @rdotpy