Refs #26605 -- Added migrations state test for a swappable model inheriting an abstract model inheriting concrete model.

Thanks Sébastien Diemer for the report and test.

tests/migrations/test_state.py

@@ -1006,6 +1006,48 @@ class ModelStateTests(SimpleTestCase):
         self.assertEqual(author_state.bases, (models.Model, ))
         self.assertEqual(author_state.managers, [])
 
+    @override_settings(TEST_SWAPPABLE_MODEL='migrations.SomeFakeModel')
+    def test_create_swappable_from_abstract(self):
+        """
+        A swappable model inheriting from a hierarchy:
+        concrete -> abstract -> concrete.
+        """
+        new_apps = Apps(['migrations'])
+
+        class SearchableLocation(models.Model):
+            keywords = models.CharField(max_length=256)
+
+        class Station(SearchableLocation):
+            name = models.CharField(max_length=128)
+
+            class Meta:
+                abstract = True
+
+        class BusStation(Station):
+            bus_routes = models.CharField(max_length=128)
+            inbound = models.BooleanField(default=False)
+
+            class Meta(Station.Meta):
+                app_label = 'migrations'
+                apps = new_apps
+                swappable = 'TEST_SWAPPABLE_MODEL'
+
+        station_state = ModelState.from_model(BusStation)
+        self.assertEqual(station_state.app_label, 'migrations')
+        self.assertEqual(station_state.name, 'BusStation')
+        self.assertEqual(
+            [x for x, y in station_state.fields],
+            ['searchablelocation_ptr', 'name', 'bus_routes', 'inbound']
+        )
+        self.assertEqual(station_state.fields[1][1].max_length, 128)
+        self.assertEqual(station_state.fields[2][1].null, False)
+        self.assertEqual(
+            station_state.options,
+            {'abstract': False, 'swappable': 'TEST_SWAPPABLE_MODEL', 'indexes': []}
+        )
+        self.assertEqual(station_state.bases, ('migrations.searchablelocation', ))
+        self.assertEqual(station_state.managers, [])
+
     @override_settings(TEST_SWAPPABLE_MODEL='migrations.SomeFakeModel')
     def test_custom_manager_swappable(self):
         """