Add or document a way to test data migrations

[Tom Linford]

At Robinhood, we've been using a custom in-house MigrationTestCase that we'd like to contribute, but want to check the API of it before contributing it. Here's the definition of the class:

class MigrationTestCase(TransactionTestCase):
    """
    app_label: name of app (ie. "users" or "polls")
    (start|dest)_migration_name: name of migration in app
        (e.g. "0001_initial")
    additional_dependencies: list of tuples of `(app_label, migration_name)`.
        Add any additional migrations here that need to be included in the
        generation of the model states.

    Usage:

    class TestCase(MigrationTestCase):
        app_label = ...
        start_migration_name = ...
        dest_migration_name = ...
        additional_dependencies = ...

        def setUp(self):
            # Create models with regular orm
            super(TestCase, self).setUp()
            # Create models with start orm. Access model with:
            # self.start_models["<app_label>"]["<model_name>"]
            # Note that model_name must be all lower case, you can just do:
            # <instance>._meta.model_name to get the model_name

        def test(self):
            # Still using start orm
            self.migrate_to_dest()
            # Now, you can access dest models with:
            # self.dest_models["<app_label>"]["<model_name>"]
    """
    app_label = None
    start_migration_name = None
    dest_migration_name = None
    additional_dependencies = []

Let me know if this API is agreeable and I can make a PR for this feature.

[Tim Graham]

The DevelopersMailingList is a better place to propose and get feedback on features like this.

[Tim Graham]

​django-developers thread

Accepting on the basis of some way to test data migrations.