Fixed #19688 -- Allow model subclassing with a custom metaclass using six.with_metaclass

tests/modeltests/base/models.py

@@ -0,0 +1,5 @@
+from django.db.models.base import ModelBase
+
+
+class CustomBaseModel(ModelBase):
+    pass

tests/modeltests/base/tests.py

@@ -0,0 +1,36 @@
+from __future__ import unicode_literals
+
+from django.db import models
+from django.test.testcases import SimpleTestCase
+from django.utils import six
+from django.utils.unittest import skipIf
+
+from .models import CustomBaseModel
+
+
+class CustomBaseTest(SimpleTestCase):
+
+    @skipIf(six.PY3, 'test metaclass definition under Python 2')
+    def test_py2_custom_base(self):
+        """
+        Make sure models.Model can be subclassed with a valid custom base
+        using __metaclass__
+        """
+        try:
+            class MyModel(models.Model):
+                __metaclass__ = CustomBaseModel
+        except Exception:
+            self.fail("models.Model couldn't be subclassed with a valid "
+                      "custom base using __metaclass__.")
+
+    def test_six_custom_base(self):
+        """
+        Make sure models.Model can be subclassed with a valid custom base
+        using `six.with_metaclass`.
+        """
+        try:
+            class MyModel(six.with_metaclass(CustomBaseModel, models.Model)):
+                pass
+        except Exception:
+            self.fail("models.Model couldn't be subclassed with a valid "
+                      "custom base using `six.with_metaclass`.")