[2.2.x] Refs #30325 -- Added tests for using count()/exists() with cu…

…stom managers and reverse M2M relations.

Backport of 9ac8520 from master

tests/many_to_many/models.py

@@ -27,13 +27,20 @@ def __str__(self):
         return self.name
 
 
+class NoDeletedArticleManager(models.Manager):
+    def get_queryset(self):
+        return super().get_queryset().exclude(headline='deleted')
+
+
 class Article(models.Model):
     headline = models.CharField(max_length=100)
     # Assign a string as name to make sure the intermediary model is
     # correctly created. Refs #20207
     publications = models.ManyToManyField(Publication, name='publications')
     tags = models.ManyToManyField(Tag, related_name='tags')
 
+    objects = NoDeletedArticleManager()
+
     class Meta:
         ordering = ('headline',)
 

tests/many_to_many/tests.py

@@ -557,3 +557,9 @@ def test_inherited_models_selects(self):
             ]
         )
         self.assertQuerysetEqual(b.publications.all(), ['<Publication: Science Weekly>'])
+
+    def test_custom_default_manager_exists_count(self):
+        a5 = Article.objects.create(headline='deleted')
+        a5.publications.add(self.p2)
+        self.assertEqual(self.p2.article_set.count(), self.p2.article_set.all().count())
+        self.assertEqual(self.p3.article_set.exists(), self.p3.article_set.all().exists())