When it comes to testing in python
pytest is my favorite testing tool.
pytest is a testing framework that strips out boilerplate and adds a whole bunch of sensible utilities to make your tests more pythonic. In this post we’ll cover how to add that awesomeness to a Django project.
This is a cross-post of a post I did for the TrackMaven Engine Room.
import unittest class TestExample(unittest.TestCase): def test_hello_world(self): self.assertEqual("hello world", "hello world")
def test_hello_world(): assert "hello_world" == "hello_world"
In our newer Django projects we’ve been using
pytest instead of the default test runner. Django’s prefer testing is built on top of unittest. Luckily for any
pytest fans, this makes it easy to have
pytest be a drop in replacement without having to change a single test.
Let’s dive into how you can setup
pytest on your Django projects. For this post, I’ve created an repo with a dummy Django 1.8 project. It’s local development environment is managed by Docker + Docker Compose.. All code examples are pulled from there.
requirements-dev.txt we’ve can add in the two packages to be installed.
We need to bootstrap
pytest with our Django project settings.
pytest-django’s documentation recommends a few different ways to achieve this. I’d advocate loading them in through a global
conftest.py files are invoked before any tests are run. They provide a convenient method to setup hooks or configure any settings for our tests.
conftest.py lives dictates the scope of where it applies. If present in the root test folder, hooks declared will apply to all tests. If present in a specific module, hooks will only apply to tests in that module.
tests/ ├── conftest.py # Applies to all tests └── example/ ├── conftest.py # Applies only to tests in this module/folder. ├── test_foo.py
In our case, we want the
conftest.py to apply to all tests therefore we place it in our tests root directory.
import os import django from django.conf import settings # We manually designate which settings we will be using in an environment variable # This is similar to what occurs in the `manage.py` os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'app.config.settings') # `pytest` automatically calls this function once when tests are run. def pytest_configure(): settings.DEBUG = False # If you have any test specific settings, you can declare them here, # e.g. # settings.PASSWORD_HASHERS = ( # 'django.contrib.auth.hashers.MD5PasswordHasher', # ) django.setup() # Note: In Django =< 1.6 you'll need to run this instead # settings.configure()
If setup correctly, you should now be able to run the test suite. Instead of running tests through
manage.py you run them through the
py.test command directly.
$ docker-compose run web py.test === test session starts === platform linux -- Python 3.3.6 -- py-1.4.30 -- pytest-2.7.2 rootdir: /code, inifile: plugins: django collected 3 items tests/integration_tests/example/test_models.py .. tests/unit_tests/example/test_helpers.py . === 3 passed in 2.95 seconds ===
To run a specific test in a module/file, you just include the path after the command, like so
$ docker-compose run web py.test tests/integration_tests/example/test_models.py === test session starts === platform linux -- Python 3.3.6 -- py-1.4.30 -- pytest-2.7.2 rootdir: /code/tests/integration_tests/example, inifile: plugins: django collected 2 items tests/integration_tests/example/test_models.py .. === 2 passed in 2.92 seconds ===
To run a specific test, point
py.test to a specific file and test name, like so
$ docker-compose run web py.test tests/integration_tests/example/test_models.py::test_save === test session starts === platform linux -- Python 3.3.6 -- py-1.4.30 -- pytest-2.7.2 rootdir: /code/tests/integration_tests/example, inifile: plugins: django collected 2 items tests/integration_tests/example/test_models.py . === 1 passed in 2.94 seconds ===
As mentioned previously, any existing Django
unittest style tests will work out of the box. Here is an example.
# Any existing `unittest` style tests still work without any changes needed. from django.test import TestCase class ExampleTestCase(TestCase): def setUp(self): self.maven = Dog(name="Maven", breed="corgi") self.maven.save() def test_save(self): self.assertEquals(self.maven.name, "Maven") # You can mix in pytest's `assert` approach! assert self.maven.breed == "corgi"
One key difference to watch out for is running
pytest style tests against the database.
pytest-django takes a conservative approach to enabling database access in tests. Any
pytest style tests will fail if they try to access the database.
In order to allow database access to a test, you need add a
py.test mark decorator like so…
from example.models import Dog import pytest # If your tests need to use the database and want to use pytest # function test approach, you need to `mark` it. @pytest.mark.django_db def test_save(): maven = Dog(name="Maven", breed="corgi") maven.save() assert maven.name == "Maven" assert maven.breed == "corgi"
That’s it! You can now take full advantage of
pytest in your Django project.