Fixed #25746 -- Isolated inlined test models registration.

Thanks to Tim for the review.

django/contrib/auth/checks.py

@@ -6,10 +6,22 @@ from django.conf import settings
 from django.core import checks
 
 
-def check_user_model(**kwargs):
-    errors = []
+def check_user_model(app_configs=None, **kwargs):
+    if app_configs is None:
+        cls = apps.get_model(settings.AUTH_USER_MODEL)
+    else:
+        app_label, model_name = settings.AUTH_USER_MODEL.split('.')
+        for app_config in app_configs:
+            if app_config.label == app_label:
+                cls = app_config.get_model(model_name)
+                break
+        else:
+            # Checks might be run against a set of app configs that don't
+            # include the specified user model. In this case we simply don't
+            # perform the checks defined below.
+            return []
 
-    cls = apps.get_model(settings.AUTH_USER_MODEL)
+    errors = []
 
     # Check that REQUIRED_FIELDS is a list
     if not isinstance(cls.REQUIRED_FIELDS, (list, tuple)):

django/contrib/contenttypes/checks.py

@@ -1,17 +1,23 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+from itertools import chain
+
 from django.apps import apps
 from django.utils import six
 
 
-def check_generic_foreign_keys(**kwargs):
+def check_generic_foreign_keys(app_configs=None, **kwargs):
     from .fields import GenericForeignKey
 
+    if app_configs is None:
+        models = apps.get_models()
+    else:
+        models = chain.from_iterable(app_config.get_models() for app_config in app_configs)
     errors = []
     fields = (obj
-        for cls in apps.get_models()
-        for obj in six.itervalues(vars(cls))
+        for model in models
+        for obj in six.itervalues(vars(model))
         if isinstance(obj, GenericForeignKey))
     for field in fields:
         errors.extend(field.check())

django/core/checks/model_checks.py

@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 
 import inspect
 import types
+from itertools import chain
 
 from django.apps import apps
 from django.core.checks import Error, Tags, register
@@ -11,21 +12,24 @@ from django.core.checks import Error, Tags, register
 @register(Tags.models)
 def check_all_models(app_configs=None, **kwargs):
     errors = []
-    for model in apps.get_models():
-        if app_configs is None or model._meta.app_config in app_configs:
-            if not inspect.ismethod(model.check):
-                errors.append(
-                    Error(
-                        "The '%s.check()' class method is "
-                        "currently overridden by %r." % (
-                            model.__name__, model.check),
-                        hint=None,
-                        obj=model,
-                        id='models.E020'
-                    )
+    if app_configs is None:
+        models = apps.get_models()
+    else:
+        models = chain.from_iterable(app_config.get_models() for app_config in app_configs)
+    for model in models:
+        if not inspect.ismethod(model.check):
+            errors.append(
+                Error(
+                    "The '%s.check()' class method is "
+                    "currently overridden by %r." % (
+                        model.__name__, model.check),
+                    hint=None,
+                    obj=model,
+                    id='models.E020'
                 )
-            else:
-                errors.extend(model.check(**kwargs))
+            )
+        else:
+            errors.extend(model.check(**kwargs))
     return errors