Renamed AppCache to Apps.

Also renamed app_cache to apps and "app cache" to "app registry".

Deprecated AppCache.app_cache_ready() in favor of Apps.ready().

tests/apps/tests.py

@@ -0,0 +1,51 @@
+from __future__ import absolute_import
+
+from django.apps import apps
+from django.apps.registry import Apps
+from django.db import models
+from django.test import TestCase
+
+from .models import TotallyNormal, SoAlternative, new_apps
+
+
+class AppsTests(TestCase):
+
+    def test_models_py(self):
+        """
+        Tests that the models in the models.py file were loaded correctly.
+        """
+        self.assertEqual(apps.get_model("apps", "TotallyNormal"), TotallyNormal)
+        self.assertEqual(apps.get_model("apps", "SoAlternative"), None)
+
+        self.assertEqual(new_apps.get_model("apps", "TotallyNormal"), None)
+        self.assertEqual(new_apps.get_model("apps", "SoAlternative"), SoAlternative)
+
+    def test_dynamic_load(self):
+        """
+        Makes a new model at runtime and ensures it goes into the right place.
+        """
+        old_models = apps.get_models(apps.get_app_config("apps").models_module)
+        # Construct a new model in a new app registry
+        body = {}
+        new_apps = Apps()
+        meta_contents = {
+            'app_label': "apps",
+            'apps': new_apps,
+        }
+        meta = type("Meta", tuple(), meta_contents)
+        body['Meta'] = meta
+        body['__module__'] = TotallyNormal.__module__
+        temp_model = type("SouthPonies", (models.Model,), body)
+        # Make sure it appeared in the right place!
+        self.assertEqual(
+            old_models,
+            apps.get_models(apps.get_app_config("apps").models_module),
+        )
+        self.assertEqual(new_apps.get_model("apps", "SouthPonies"), temp_model)
+
+    def test_singleton_master(self):
+        """
+        Ensures that only one master registry can exist.
+        """
+        with self.assertRaises(RuntimeError):
+            Apps(master=True)