Deprecated load_app().

Adjusted several tests that used it to add apps to the app cache and
then attempted to remove them by manipulating attributes directly.

Also renamed invalid_models to invalid_models_tests to avoid clashing
application labels between the outer and the inner invalid_models
applications.

tests/proxy_model_inheritance/tests.py

@@ -3,7 +3,6 @@ from __future__ import unicode_literals
 import os
 import sys
 
-from django.conf import settings
 from django.core.apps import app_cache
 from django.core.management import call_command
 from django.test import TestCase, TransactionTestCase
@@ -21,28 +20,21 @@ class ProxyModelInheritanceTests(TransactionTestCase):
     for the proxied model (as described in #12286).  This test creates two dummy
     apps and calls migrate, then verifies that the table has been created.
     """
-
-    available_apps = []
+    available_apps = ['app1', 'app2']
 
     def setUp(self):
         self.old_sys_path = sys.path[:]
         sys.path.append(os.path.dirname(os.path.abspath(upath(__file__))))
-        for app in settings.INSTALLED_APPS:
-            app_cache.load_app(app)
+        self._with_app1 = app_cache._begin_with_app('app1')
+        self._with_app2 = app_cache._begin_with_app('app2')
 
     def tearDown(self):
+        app_cache._end_with_app(self._with_app1)
+        app_cache._end_with_app(self._with_app2)
         sys.path = self.old_sys_path
-        del app_cache.app_configs['app1']
-        del app_cache.app_configs['app2']
-        del app_cache.all_models['app1']
-        del app_cache.all_models['app2']
 
     def test_table_exists(self):
-        try:
-            app_cache.set_available_apps(settings.INSTALLED_APPS)
-            call_command('migrate', verbosity=0)
-        finally:
-            app_cache.unset_available_apps()
+        call_command('migrate', verbosity=0)
         from .app1.models import ProxyModel
         from .app2.models import NiceModel
         self.assertEqual(NiceModel.objects.all().count(), 0)
@@ -56,7 +48,6 @@ class MultiTableInheritanceProxyTest(TestCase):
         Deleting an instance of a model proxying a multi-table inherited
         subclass should cascade delete down the whole inheritance chain (see
         #18083).
-
         """
         instance = ConcreteModelSubclassProxy.objects.create()
         instance.delete()