Getting Started with Testing in Django

Following yesterday's post another hotly requested topic was testing in Django. Today I wanted to give a simple overview on how to get started writing tests for your Django applications. Since Django 1.1, Django has automatically provided a tests.py file when you create a new application, that's where we'll start.

For me the first thing I want to test with my applications is, "Do the views work?". This makes sense, the views are what the user sees, they need to at least be in a working state (200 OK response) before anything else can happen (business logic). So the most basic thing you can do to start testing is something like this:

    from django.tests import TestCase
    class MyTests(TestCase):
        def test_views(self):
            response = self.client.get("/my/url/")
            self.assertEqual(response.status_code, 200)

By just making sure you run this code before you commit something you've already eliminated a bunch of errors, syntax errors in your URLs or views, typos, forgotten imports, etc. The next thing I like to test is making sure that all the branches of my code are covered, the most common place my views have branches is in views that handle forms, one branch for GET and one for POST. So I'll write a test like this:

    from django.tests import TestCase
    class MyTests(TestCase):
        def test_forms(self):
            response = self.client.get("/my/form/")
            self.assertEqual(response.status_code, 200)
            
            response = self.client.post("/my/form/", {"data": "value"})
            self.assertEqual(response.status_code, 302) # Redirect on form success
            
            response = self.client.post("/my/form/", {})
            self.assertEqual(response.status_code, 200) # we get our page back with an error

Now I've tested both the GET and POST conditions on this view, as well the form is valid and form is invalid cases. With this strategy you can have a good base set of tests for any application with not a lot of work. The next step is setting up tests for your business logic. These are a little more complicated, you need to make sure models are created and edited in the right cases, emails are sent in the right places, etc. Django's testing documentation is a great place to read more on writing tests for your applications.

Running the Django Test Suite

This question came up in IRC yesterday, so I figured I'd run through it today. Django has a very extensive test suite that tests all of the components of Django itself. If you've ever written a patch for Django you probably know that tests are a requirement, for both new features and bug fixes. I'm going to try to run down how to setup your own testing envrioment.

First you need to have Django installed somewhere, for now I'll assume you have it in ~/django_src/. Somewhere on your python path, go ahead are use django-admin.py to create a new project. I've named this project django_test. Next, inside of that project create a folder named settings, and move settings.py into that folder and renmae it __init__.py. The reason we're going to have a settings directory is so that we can have subsettings for individual scenarios. Put some default settings for the various field in there now, for example my default settings provides the necessary options for SQLite. Now if there are any other subsettings you wish to setup create a file for them in the settings directory, and at the top of this file put from django_test.settings import *, followed by whatever settings you wish to overide. For example I have a mysql.py that overides my default SQLite database settings with MySQL values.

Now that we have our test settings, go to the directory where you have Django installed. To run the tests do ./tests/runtests.py --settings=django_test.settings. You can also use the DJANGO_SETTINGS_MODULE enviromental variable in place of passing in the settings like this. You can also provide a verbosity argument, the default is 0, I prefer to run with verbosity=1 because this keeps you up to date on the progress of the tests, without too much extraneus output.

Usually when you are working on a patch you don't need to run the entire test suite, your patch only affects a few tests. Therefore, you can provide a list of tests you'd like to run, so for example you could do ./tests/runtests.py --settings=django_test.settings.mysql -v 1 model_forms model_formsets. This will run the model_forms and model_formsets tests, with your mysql settings, at verbosity level 1.

And that's all it takes to run the Django test suite.