Django pratical test tool

Testing Django may seems complicated sometimes, and especially with some django features full of encapsulation. This can be easily fixed by some python tricks.

Testing an admin function

Admin classes are initialized by Django directly. The trick here is to override the init method.

def setUp(self):
    MyAdminClass.__init__ = lambda x: None
    my_admin_object = MyAdminClass()

Testing a template tag

The same kind of trick can be applied to test template tag with parameters.

def new_init(self, value, user):
    self.value = value
    self.user = user

def setUp(self):
    MyTemplateTagNode.__init__ = new_init
    value = "my value"
    my_user = User.objects.get(id=1)
    node = MyTemplateTagNode(my_value, my_user))

Testing complex view

Sometimes some view may rely on external services or request and you don’t want to rely on anything external when performing unit tests.

class MyComplexView(BaseView):

     det get(self, *args, **kwargs):
          ...
          my_external_object = ExternalObject()
          ...

You will need sometimes to redesign your code especially to be able to test it.

class MyComplexView(BaseView):

    def get_external_object(self):
        return ExternalObject()

     det get(self, *args, **kwargs):
          ...
          my_external_object = self.get_external_object()
          ...

Then, in your setup method, just do:

def get_external_object(self):
    # Return an object implementing the right protocol
    return MockExternalObject()

def setup(self):
    MyComplexView.get_external_object = get_external_object

Testing dynamic type creation

If you need to test an exception is raised when a class in defined (Imagine something like django model) you will have to use the type trick.

Encapsulate your class creation in a function (sample extract from the csv_importer application):

def create_unexpected_model():
    return type('TestCsvDBUnmatchingModel', CsvModel, {'name': CharField(unexpected=True)})

then you can use assertRaises

self.assertRaises(ValueError, create_unexpected_model)    

Handling data

On a growing project, managing data through fixture can be really painful. Easy with django-dynamic-fixture.

A good advice is to create your own service to wrap the data creation into a more readable and usable API usage.

user = GenerateUser().create_admin()

Testing email content and formatting

By default, django override some settings when using emails in testing. If you need to automatically generate email through a smtp server, you will have to change the settings just before performing the test.

For this, I use the following context manager:

class EmailSettingChange(object):
    """ 
    Change the email setting to not use the locmem backend
    but send real email
    """

    def __init__(self):
	self.original_email_backend = settings.EMAIL_BACKEND

    def __enter__(self):
	if hasattr(settings, 'TEST_SEND_EMAIL') and settings.TEST_SEND_EMAIL:
	    settings.EMAIL_BACKEND = settings.TEST_SEND_EMAIL_CONF['EMAIL_BACKEND']
	    settings.EMAIL_HOST = settings.TEST_SEND_EMAIL_CONF['EMAIL_HOST']
	    settings.EMAIL_HOST_USER = settings.TEST_SEND_EMAIL_CONF['EMAIL_HOST_USER']
	    settings.EMAIL_HOST_PASSWORD = settings.TEST_SEND_EMAIL_CONF['EMAIL_HOST_PASSWORD']
	    settings.EMAIL_PORT = settings.TEST_SEND_EMAIL_CONF['EMAIL_PORT']
	    settings.EMAIL_USE_TLS = settings.TEST_SEND_EMAIL_CONF['EMAIL_USE_TLS']

    def __exit__(self, type, value, tb):
	settings.EMAIL_BACKEND = self.original_email_backend

Testing rollback

If you need to test than rollbacking is working correctly in your application, you can’t do that with a django test case, you have to use a TransactionTestCase. Take care to manually commit at the end of your setup method.

More information in the django doc