Fixed #25172 -- Fixed check framework to work with multiple databases.

tests/invalid_models_tests/test_backend_specific.py

@@ -1,37 +1,31 @@
 # -*- encoding: utf-8 -*-
 from __future__ import unicode_literals
 
-from types import MethodType
-
 from django.core.checks import Error
-from django.db import connection, models
+from django.db import connections, models
+from django.test import mock
 
 from .base import IsolatedModelsTestCase
 
 
+def dummy_allow_migrate(db, app_label, **hints):
+    # Prevent checks from being run on the 'other' database, which doesn't have
+    # its check_field() method mocked in the test.
+    return db == 'default'
+
+
 class BackendSpecificChecksTests(IsolatedModelsTestCase):
 
+    @mock.patch('django.db.models.fields.router.allow_migrate', new=dummy_allow_migrate)
     def test_check_field(self):
         """ Test if backend specific checks are performed. """
-
         error = Error('an error', hint=None)
 
-        def mock(self, field, **kwargs):
-            return [error]
-
         class Model(models.Model):
             field = models.IntegerField()
 
         field = Model._meta.get_field('field')
-
-        # Mock connection.validation.check_field method.
-        v = connection.validation
-        old_check_field = v.check_field
-        v.check_field = MethodType(mock, v)
-        try:
+        with mock.patch.object(connections['default'].validation, 'check_field', return_value=[error]):
             errors = field.check()
-        finally:
-            # Unmock connection.validation.check_field method.
-            v.check_field = old_check_field
 
         self.assertEqual(errors, [error])