Refs #29721 -- Simplified migration used to test atomic recording.

This makes sure atomic recording of migration application is used when
the schema editor doesn't defer any statement.

tests/migrations/test_executor.py

@@ -1,11 +1,12 @@
 from unittest import mock
 
 from django.apps.registry import apps as global_apps
-from django.db import DatabaseError, connection
+from django.db import DatabaseError, connection, migrations, models
 from django.db.migrations.exceptions import InvalidMigrationPlan
 from django.db.migrations.executor import MigrationExecutor
 from django.db.migrations.graph import MigrationGraph
 from django.db.migrations.recorder import MigrationRecorder
+from django.db.migrations.state import ProjectState
 from django.test import (
     SimpleTestCase, modify_settings, override_settings, skipUnlessDBFeature,
 )
@@ -655,18 +656,33 @@ class ExecutorTests(MigrationTestBase):
     # When the feature is False, the operation and the record won't be
     # performed in a transaction and the test will systematically pass.
     @skipUnlessDBFeature('can_rollback_ddl')
-    @override_settings(MIGRATION_MODULES={'migrations': 'migrations.test_migrations'})
     def test_migrations_applied_and_recorded_atomically(self):
         """Migrations are applied and recorded atomically."""
+        class Migration(migrations.Migration):
+            operations = [
+                migrations.CreateModel('model', [
+                    ('id', models.AutoField(primary_key=True)),
+                ]),
+            ]
+
         executor = MigrationExecutor(connection)
         with mock.patch('django.db.migrations.executor.MigrationExecutor.record_migration') as record_migration:
             record_migration.side_effect = RuntimeError('Recording migration failed.')
             with self.assertRaisesMessage(RuntimeError, 'Recording migration failed.'):
+                executor.apply_migration(
+                    ProjectState(),
+                    Migration('0001_initial', 'record_migration'),
+                )
                 executor.migrate([('migrations', '0001_initial')])
         # The migration isn't recorded as applied since it failed.
         migration_recorder = MigrationRecorder(connection)
-        self.assertFalse(migration_recorder.migration_qs.filter(app='migrations', name='0001_initial').exists())
-        self.assertTableNotExists('migrations_author')
+        self.assertIs(
+            migration_recorder.migration_qs.filter(
+                app='record_migration', name='0001_initial',
+            ).exists(),
+            False,
+        )
+        self.assertTableNotExists('record_migration_model')
 
 
 class FakeLoader: