django-test-migrations
Features
- Allows to test
djangoschema and data migrations - Allows to test both forward and rollback migrations
- Allows to test the migrations order
- Allows to test migration names
- Allows to test database configuration
- Fully typed with annotations and checked with
mypy, PEP561 compatible - Easy to start: has lots of docs, tests, and tutorials
Read the announcing post. See real-world usage example.
Installation
pip install django-test-migrations
We support several django versions:
1.112.23.03.1
Other versions might work too, but they are not officially supported.
Testing django migrations
Testing migrations is not a frequent thing in django land. But, sometimes it is totally required. When?
When we do complex schema or data changes and what to be sure that existing data won't be corrupted. We might also want to be sure that all migrations can be safely rolled back. And as a final touch we want to be sure that migrations are in the correct order and have correct dependencies.
Testing forward migrations
To test all migrations we have a Migrator class.
It has three methods to work with:
-
.apply_initial_migration()which takes app and migration names to generate a state before the actual migration happens. It creates thebefore stateby applying all migrations up to and including the ones passed as an argument. -
.apply_tested_migration()which takes app and migration names to perform the actual migration -
.reset()to clean everything up after we are done with testing
So, here's an example:
from django_test_migrations.migrator import Migrator
migrator = Migrator(database='default')
# Initial migration, currently our model has only a single string field:
# Note:
# We are testing migration `0002_someitem_is_clean`, so we are specifying
# the name of the previous migration (`0001_initial`) in the
# .apply_initial_migration() method in order to prepare a state of the database
# before applying the migration we are going to test.
#
old_state = migrator.apply_initial_migration(('main_app', '0001_initial'))
SomeItem = old_state.apps.get_model('main_app', 'SomeItem')
# Let's create a model with just a single field specified:
SomeItem.objects.create(string_field='a')
assert len(SomeItem._meta.get_fields()) == 2 # id + string_field
# Now this migration will add `is_clean` field to the model:
new_state = migrator.apply_tested_migration(
('main_app', '0002_someitem_is_clean'),
)
SomeItem = new_state.apps.get_model('main_app', 'SomeItem')
# We can now test how our migration worked, new field is there:
assert SomeItem.objects.filter(is_clean=True).count() == 0
assert len(SomeItem._meta.get_fields()) == 3 # id + string_field + is_clean
# Cleanup:
migrator.reset()
That was an example of a forward migration.
Backward migration
The thing is that you can also test backward migrations. Nothing really changes except migration names that you pass and your logic:
migrator = Migrator()
# Currently our model has two field, but we need a rollback:
old_state = migrator.apply_initial_migration(
('main_app', '0002_someitem_is_clean'),
)
SomeItem = old_state.apps.get_model('main_app', 'SomeItem')
# Create some data to illustrate your cases:
# ...
# Now this migration will drop `is_clean` field:
new_state = migrator.apply_tested_migration(('main_app', '0001_initial'))
# Assert the results:
# ...
# Cleanup:
migrator.reset()
Testing migrations ordering
Sometimes we also want to be sure that our migrations are in the correct order. And all our dependecies = [...] are correct.
To achieve that we have plan.py module.
That's how it can be used:
from django_test_migrations.plan import all_migrations, nodes_to_tuples
main_migrations = all_migrations('default', ['main_app', 'other_app'])
assert nodes_to_tuples(main_migrations) == [
('main_app', '0001_initial'),
('main_app', '0002_someitem_is_clean'),
('other_app', '0001_initial'),
('main_app', '0003_update_is_clean'),
('main_app', '0004_auto_20191119_2125'),
('other_app', '0002_auto_20191120_2230'),
]
This way you can be sure that migrations and apps that depend on each other will be executed in the correct order.
Test framework integrations
🐍
We support several test frameworks as first-class citizens. That's a testing tool after all!
Note that the Django post_migrate signal's receiver list is cleared at the start of tests and restored afterwards. If you need to test your own post_migrate signals then attach/remove them during a test.
pytest
We ship django-test-migrations with a pytest plugin that provides two convinient fixtures:
migrator_factorythat gives you an opportunity to createMigratorclasses for any databasemigratorinstance for the'default'database
That's how it can be used:
import pytest
@pytest.mark.django_db()
def test_pytest_plugin_initial(migrator):
"""Ensures that the initial migration works."""
old_state = migrator.apply_initial_migration(('main_app', None))
with pytest.raises(LookupError):
# Models does not yet exist:
old_state.apps.get_model('main_app', 'SomeItem')
new_state = migrator.apply_tested_migration(('main_app', '0001_initial'))
# After the initial migration is done, we can use the model state:
SomeItem = new_state.apps.get_model('main_app', 'SomeItem')
assert SomeItem.objects.filter(string_field='').count() == 0
unittest
We also ship an integration with the built-in unittest framework.
Here's how it can be used:
from django_test_migrations.contrib.unittest_case import MigratorTestCase
class TestDirectMigration(MigratorTestCase):
"""This class is used to test direct migrations."""
migrate_from = ('main_app', '0002_someitem_is_clean')
migrate_to = ('main_app', '0003_update_is_clean')
def prepare(self):
"""Prepare some data before the migration."""
SomeItem = self.old_state.apps.get_model('main_app', 'SomeItem')
SomeItem.objects.create(string_field='a')
SomeItem.objects.create(string_field='a b')
def test_migration_main0003(self):
"""Run the test itself."""
SomeItem = self.new_state.apps.get_model('main_app', 'SomeItem')
assert SomeItem.objects.count() == 2
assert SomeItem.objects.filter(is_clean=True).count() == 1
Choosing only migrations tests
In CI systems it is important to get instant feedback. Running tests that apply database migration can slow down tests execution, so it is often a good idea to run standard, fast, regular unit tests without migrations in parallel with slower migrations tests.
pytest
django_test_migrations adds migration_test marker to each test using migrator_factory or migrator fixture. To run only migrations test, use -m option:
pytest -m migration_test # runs only migraion tests
pytest -m "not migration_test" # runs all except migraion tests
unittest
django_test_migrations adds migration_test tag to every MigratorTestCase subclass. To run only migrations tests, use --tag option:
python mange.py test --tag=migration_test # runs only migraion tests
python mange.py test --exclude-tag=migration_test # runs all except migraion tests
Django Checks
django_test_migrations comes with 2 groups of Django's checks for:
- detecting migrations scripts automatically generated names
- validating some subset of database settings
Testing migration names
django generates migration names for you when you run makemigrations. And these names are bad (read more about why it is bad)! Just look at this: 0004_auto_20191119_2125.py
What does this migration do? What changes does it have?
One can also pass --name attribute when creating migrations, but it is easy to forget.
We offer an automated solution: django check that produces an error for each badly named migration.
Add our check into your INSTALLED_APPS:
INSTALLED_APPS = [
# ...
# Our custom check:
'django_test_migrations.contrib.django_checks.AutoNames',
]
And then in your CI run:
python manage.py check --deploy
This way you will be safe from wrong names in your migrations.
Do you have a migrations that cannot be renamed? Add them to the ignore list:
# settings.py
DTM_IGNORED_MIGRATIONS = {
('main_app', '0004_auto_20191119_2125'),
('dependency_app', '0001_auto_20201110_2100'),
}
And we won't complain about them.
Or you can completely ignore entire app:
# settings.py
DTM_IGNORED_MIGRATIONS = {
('dependency_app', '*'),
('another_dependency_app', '*'),
}
Database configuration
Add our check to INSTALLED_APPS:
INSTALLED_APPS = [
# ...
# Our custom check:
'django_test_migrations.contrib.django_checks.DatabaseConfiguration',
]
Then just run check management command in your CI like listed in section above.
Related projects
You might also like:
- django-migration-linter - Detect backward incompatible migrations for your django project.
- wemake-django-template - Bleeding edge django template focused on code quality and security with both
django-test-migrationsanddjango-migration-linteron board.
Credits
This project is based on work of other awesome people:
License
MIT.
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