refactor migration test case

src/documents/tests/utils.py

@@ -4,7 +4,10 @@ import tempfile
 from collections import namedtuple
 from contextlib import contextmanager
 
-from django.test import override_settings
+from django.apps import apps
+from django.db import connection
+from django.db.migrations.executor import MigrationExecutor
+from django.test import override_settings, TransactionTestCase
 
 
 def setup_directories():
@@ -79,3 +82,38 @@ class DirectoriesMixin:
     def tearDown(self) -> None:
         super(DirectoriesMixin, self).tearDown()
         remove_dirs(self.dirs)
+
+
+class TestMigrations(TransactionTestCase):
+
+    @property
+    def app(self):
+        return apps.get_containing_app_config(type(self).__module__).name
+
+    migrate_from = None
+    migrate_to = None
+
+    def setUp(self):
+        super(TestMigrations, self).setUp()
+
+        assert self.migrate_from and self.migrate_to, \
+            "TestCase '{}' must define migrate_from and migrate_to     properties".format(type(self).__name__)
+        self.migrate_from = [(self.app, self.migrate_from)]
+        self.migrate_to = [(self.app, self.migrate_to)]
+        executor = MigrationExecutor(connection)
+        old_apps = executor.loader.project_state(self.migrate_from).apps
+
+        # Reverse to the original migration
+        executor.migrate(self.migrate_from)
+
+        self.setUpBeforeMigration(old_apps)
+
+        # Run the migration to test
+        executor = MigrationExecutor(connection)
+        executor.loader.build_graph()  # reload.
+        executor.migrate(self.migrate_to)
+
+        self.apps = executor.loader.project_state(self.migrate_to).apps
+
+    def setUpBeforeMigration(self, apps):
+        pass