[1.9.x] Fixed #26186 -- Documented how app relative relationships of abstract models behave.

This partially reverts commit bc7d201bdbaeac14a49f51a9ef292d6312b4c45e.

Thanks Tim for the review.

Refs #25858.

Backport of 0223e213dd690b6b6e0669f836a20efb10998c83 from master

1 files changed, 38 insertions, 28 deletions

diff --git a/tests/model_fields/tests.py b/tests/model_fields/tests.py
index 5aafdb2844..cc6639b032 100644
--- a/tests/model_fields/tests.py
+++ b/tests/model_fields/tests.py
@@ -251,24 +251,29 @@ class ForeignKeyTests(test.TestCase):
     def test_abstract_model_app_relative_foreign_key(self):
         test_apps = Apps(['model_fields', 'model_fields.tests'])
 
-        class Refered(models.Model):
-            class Meta:
-                apps = test_apps
-                app_label = 'model_fields'
-
         class AbstractReferent(models.Model):
             reference = models.ForeignKey('Refered', on_delete=models.CASCADE)
 
             class Meta:
+                apps = test_apps
                 app_label = 'model_fields'
                 abstract = True
 
-        class ConcreteReferent(AbstractReferent):
-            class Meta:
-                apps = test_apps
-                app_label = 'tests'
+        def assert_app_model_resolved(label):
+            class Refered(models.Model):
+                class Meta:
+                    apps = test_apps
+                    app_label = label
+
+            class ConcreteReferent(AbstractReferent):
+                class Meta:
+                    apps = test_apps
+                    app_label = label
+
+            self.assertEqual(ConcreteReferent._meta.get_field('reference').related_model, Refered)
 
-        self.assertEqual(ConcreteReferent._meta.get_field('reference').related_model, Refered)
+        assert_app_model_resolved('model_fields')
+        assert_app_model_resolved('tests')
 
 
 class ManyToManyFieldTests(test.SimpleTestCase):
@@ -295,33 +300,38 @@ class ManyToManyFieldTests(test.SimpleTestCase):
     def test_abstract_model_app_relative_foreign_key(self):
         test_apps = Apps(['model_fields', 'model_fields.tests'])
 
-        class Refered(models.Model):
+        class AbstractReferent(models.Model):
+            reference = models.ManyToManyField('Refered', through='Through')
+
             class Meta:
                 apps = test_apps
                 app_label = 'model_fields'
+                abstract = True
 
-        class Through(models.Model):
-            refered = models.ForeignKey('Refered', on_delete=models.CASCADE)
-            referent = models.ForeignKey('tests.ConcreteReferent', on_delete=models.CASCADE)
+        def assert_app_model_resolved(label):
+            class Refered(models.Model):
+                class Meta:
+                    apps = test_apps
+                    app_label = label
 
-            class Meta:
-                apps = test_apps
-                app_label = 'model_fields'
+            class Through(models.Model):
+                refered = models.ForeignKey('Refered', on_delete=models.CASCADE)
+                referent = models.ForeignKey('ConcreteReferent', on_delete=models.CASCADE)
 
-        class AbstractReferent(models.Model):
-            reference = models.ManyToManyField('Refered', through='Through')
+                class Meta:
+                    apps = test_apps
+                    app_label = label
 
-            class Meta:
-                app_label = 'model_fields'
-                abstract = True
+            class ConcreteReferent(AbstractReferent):
+                class Meta:
+                    apps = test_apps
+                    app_label = label
 
-        class ConcreteReferent(AbstractReferent):
-            class Meta:
-                apps = test_apps
-                app_label = 'tests'
+            self.assertEqual(ConcreteReferent._meta.get_field('reference').related_model, Refered)
+            self.assertEqual(ConcreteReferent.reference.through, Through)
 
-        self.assertEqual(ConcreteReferent._meta.get_field('reference').related_model, Refered)
-        self.assertEqual(ConcreteReferent.reference.through, Through)
+        assert_app_model_resolved('model_fields')
+        assert_app_model_resolved('tests')
 
 
 class TextFieldTests(test.TestCase):