Django: How to create a model dynamically just for testing

muhuk_42188 0
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I have a Django app that requires a settings attribute in the form of:

RELATED_MODELS = ('appname1.modelname1.attribute1',
                  'appname1.modelname2.attribute2', 
                  'appname2.modelname3.attribute3', ...)

Then hooks their post_save signal to update some other fixed model depending on the attributeN defined.

I would like to test this behaviour and tests should work even if this app is the only one in the project (except for its own dependencies, no other wrapper app need to be installed). How can I create and attach/register/activate mock models just for the test database? (or is it possible at all?)

Solutions that allow me to use test fixtures would be great.

mocking unit-testing django-models django python
11 Answers

You can put your tests in a tests/ subdirectory of the app (rather than a tests.py file), and include a tests/models.py with the test-only models.

Then provide a test-running script (example) that includes your tests/ "app" in INSTALLED_APPS. (This doesn't work when running app tests from a real project, which won't have the tests app in INSTALLED_APPS, but I rarely find it useful to run reusable app tests from a project, and Django 1.6+ doesn't by default.)

(NOTE: The alternative dynamic method described below only works in Django 1.1+ if your test case subclasses TransactionTestCase - which slows down your tests significantly - and no longer works at all in Django 1.7+. It's left here only for historical interest; don't use it.)

At the beginning of your tests (i.e. in a setUp method, or at the beginning of a set of doctests), you can dynamically add "myapp.tests" to the INSTALLED_APPS setting, and then do this:

from django.core.management import call_command
from django.db.models import loading
loading.cache.loaded = False
call_command('syncdb', verbosity=0)

Then at the end of your tests, you should clean up by restoring the old version of INSTALLED_APPS and clearing the app cache again.

This class encapsulates the pattern so it doesn't clutter up your test code quite as much.

Carl_Meyer_32070

Someone already mentioned Django ticket #7835, but there appears to be a more recent reply that looks much more promising for more recent versions of Django. Specifically #42, which proposes a different TestRunner:

from importlib.util import find_spec
import unittest

from django.apps import apps
from django.conf import settings
from django.test.runner import DiscoverRunner


class TestLoader(unittest.TestLoader):
    """ Loader that reports all successful loads to a runner """
    def __init__(self, *args, runner, **kwargs):
        self.runner = runner
        super().__init__(*args, **kwargs)

    def loadTestsFromModule(self, module, pattern=None):
        suite = super().loadTestsFromModule(module, pattern)
        if suite.countTestCases():
            self.runner.register_test_module(module)
        return suite


class RunnerWithTestModels(DiscoverRunner):
    """ Test Runner that will add any test packages with a 'models' module to INSTALLED_APPS.
        Allows test only models to be defined within any package that contains tests.
        All test models should be set with app_label = 'tests'
    """
    def __init__(self, *args, **kwargs):
        self.test_packages = set()
        self.test_loader = TestLoader(runner=self)
        super().__init__(*args, **kwargs)

    def register_test_module(self, module):
        self.test_packages.add(module.__package__)

    def setup_databases(self, **kwargs):
        # Look for test models
        test_apps = set()
        for package in self.test_packages:
            if find_spec('.models', package):
                test_apps.add(package)
        # Add test apps with models to INSTALLED_APPS that aren't already there
        new_installed = settings.INSTALLED_APPS + tuple(ta for ta in test_apps if ta not in settings.INSTALLED_APPS)
        apps.set_installed_apps(new_installed)
        return super().setup_databases(**kwargs)
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