Test Django data migrations

test_django_data_migration.py

"""
Test (data) migrations in Django.

This uses py.test/pytest-django (the `transactional_db` fixture comes from there),
but could be easily adopted for Django's testrunner:

    from django.test.testcases import TransactionTestCase

    class FooTestcase(TransactionTestCase):
        def test_with_django(self):
        …

This example tests that some fields are properly migrated from a `Profile` model
to `User`.
"""

from django.db import connection
from django.db.migrations.executor import MigrationExecutor


def test_migrate_profile_to_user(transactional_db):
    executor = MigrationExecutor(connection)
    app = "YOUR_APP"
    migrate_from = [(app, "000X_before")]
    migrate_to = [(app, "000X_after")]

    executor.migrate(migrate_from)
    old_apps = executor.loader.project_state(migrate_from).apps

    # Create some old data.
    Profile = old_apps.get_model(app, "Profile")
    old_profile = Profile.objects.create(email="email",
                                         firstname="firstname",
                                         lastname="lastname")
    # Migrate forwards.
    executor.loader.build_graph()  # reload.
    executor.migrate(migrate_to)
    new_apps = executor.loader.project_state(migrate_to).apps

    # Test the new data.
    Profile = new_apps.get_model(app, "Profile")
    User = new_apps.get_model(app, "UserEntry")
    assert 'firstname' not in Profile._meta.get_all_field_names()

    user = User.objects.get(email='email')
    profile = Profile.objects.get(user__email='email')
    assert user.profile.pk == old_profile.pk == profile.pk
    assert profile.user.email == 'email'
    assert profile.user.first_name == 'firstname'
    assert profile.user.last_name == 'lastname'

Just a note for anyone thinking of using the code from https://www.caktusgroup.com/blog/2016/02/02/writing-unit-tests-django-migrations/, it doesn't work on Django 1.9 (haven't tried other versions). More specifically the data entered before the migration ran simply isn't available to the migration at all.

Why not have old_apps and new_apps set in self.setUp() rather than executing them every time they're accessed?

I added a "reusable" pytest fixture over here: https://gist.github.com/asfaltboy/b3e6f9b5d95af8ba2cc46f2ba6eae5e2

Note: https://www.caktusgroup.com/blog/2016/02/02/writing-unit-tests-django-migrations/ the code in this article misses the following line:

self.executor.loader.build_graph()

If, let's say, you create a table in the migration, you'll need this line to work properly otherwise Django will prompt django.db.utils.OperationalError: no such table

I've updated @asfaltboy's pytest fixture for django 1.8, pytest==3.0.7, pytest-django==3.1.2. At least I had problems with it which are fixed in my version: https://gist.github.com/TauPan/aec52e398d7288cb5a62895916182a9f

I tried using the medium post code, but ended up constantly getting django.db.migrations.exceptions.NodeNotFoundError: Node ('mysite.myapp', '0006_auto_20170525_2235') not a valid node when calling things like Entry = apps.get_model('mysite.myapp', 'Entry') with a migrate_from = '0006_auto_20170525_2235' (which exists as file in the migrations dir)

I have the same problem as @Pomax 😕

Never mind. I think that it's because of the fact that I have migrations disabled in my settings_test.py file..

🙈

What to do if I have not reversible migrations? How to prevent migrations before tests?

If you want to disable all migrations for regular test code and also want to test migration scenario, you can try this.
Any feedback would be welcome and I explained this at https://stackoverflow.com/a/46312855/2951749
The code base is here https://www.caktusgroup.com/blog/2016/02/02/writing-unit-tests-django-migrations/

settings.py

MIGRATION_MODULES = {app: None for app in INSTALLED_APPS}

Test.py

class TestMigrations(TestCase):
    origin_modules = getattr(settings, 'MIGRATION_MODULES', {})
    setattr(settings, 'MIGRATION_MODULES', {})
    
    ...

    @classmethod
    def tearDownClass(cls):
        setattr(settings, 'MIGRATION_MODULES', cls.origin_modules)
        super().tearDownClass()

Thanks @TauPan your version worked for me on Django 2.0 too.

Unfortunately, there is no support for pytest.raises for exceptions that occur during migrations, and possibly other issues, let's try to discuss it over at pytest-dev/pytest-django#593

EDIT: I used @TauPan's updates (Gist-spection!) and cleaned my own fork a bit and allowed specifying a list of target migrations (when conditions span across multiple apps).

I have made a pypi package out of this gist with some extra features.
Check it out: https://github.com/wemake-services/django-test-migrations