InvalidBasesError when using proxy model trigger pattern with a secondary DB configured with TEST.MIGRATE = False

[pai-danielkleinridder]

When adding a trigger to a default many-to-many "through" model (e.g. User.groups.through), running manage.py test raises InvalidBasesError if there is a secondary database that has "TEST": { "MIGRATE": False } configured.

Steps to reproduce

# settings.py
DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "django_demo_app",
        ...
    },
    "timescale": {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "django_demo_app",
        ...
        "MIGRATE": False,
        "TEST": {
            "MIGRATE": False,
        }
    },
}

# models.py
from django.contrib.auth.models import User
import pgtrigger

class UserGroupTriggers(User.groups.through):
    class Meta:
        proxy = True
        triggers = [
            pgtrigger.Protect(
                name="protect_managed_groupprops_delete",
                operation=pgtrigger.Delete,
            ),
        ]

When python manage.py test is executed, a django.db.migrations.exceptions.InvalidBasesError is thrown:

Click to view Stacktrace

Found 1 test(s).
Creating test database for alias 'default'...
Got an error creating the test database: database "test_django_demo_app" already exists
Destroying old test database for alias 'default'...
Creating test database for alias 'timescale'...
Got an error creating the test database: database "test_django_demo_app" already exists
Destroying old test database for alias 'timescale'...
Traceback (most recent call last):
  File "/Users/daniel/tmp/demo/./manage.py", line 23, in 
    main()
  File "/Users/daniel/tmp/demo/./manage.py", line 19, in main
    execute_from_command_line(sys.argv)
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/__init__.py", line 443, in execute_from_command_line
    utility.execute()
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/__init__.py", line 437, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/commands/test.py", line 24, in run_from_argv
    super().run_from_argv(argv)
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/base.py", line 420, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/base.py", line 464, in execute
    output = self.handle(*args, **options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/commands/test.py", line 63, in handle
    failures = test_runner.run_tests(test_labels)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/test/runner.py", line 1127, in run_tests
    old_config = self.setup_databases(
                 ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/test/runner.py", line 1026, in setup_databases
    return _setup_databases(
           ^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/test/utils.py", line 207, in setup_databases
    connection.creation.create_test_db(
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/db/backends/base/creation.py", line 85, in create_test_db
    call_command(
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/__init__.py", line 195, in call_command
    return command.execute(*args, **defaults)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/base.py", line 464, in execute
    output = self.handle(*args, **options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/base.py", line 111, in wrapper
    res = handle_func(*args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/core/management/commands/migrate.py", line 300, in handle
    pre_migrate_apps = pre_migrate_state.apps
                       ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/utils/functional.py", line 47, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
                                         ^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/db/migrations/state.py", line 591, in apps
    return StateApps(self.real_apps, self.models)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/db/migrations/state.py", line 652, in __init__
    self.render_multiple([*models.values(), *self.real_models])
  File "/Users/daniel/tmp/demo/.venv/lib/python3.12/site-packages/django/db/migrations/state.py", line 694, in render_multiple
    raise InvalidBasesError(
django.db.migrations.exceptions.InvalidBasesError: Cannot resolve bases for []
This can happen if you are inheriting models from an app with migrations (e.g. contrib.auth)
 in an app with no migrations; see https://docs.djangoproject.com/en/6.0/topics/migrations/#dependencies for more

I looked a little bit into why this error occurs and as far as I understand, it might be from django/db/backends/base/creation.py in create_test_db. It explicitly sets settings.MIGRATION_MODULES to None for all installed apps: Link to source code

This might be a issue with django itself, but I still wanted to create an issue here first, since the M2M through-tables pattern is in the django-pgtrigger documentation.

Environment:

Python: 3.12.9
Django: 6.0.3
django-pgtrigger: 4.17.0