Restructure our python module. A lot.

src/pretix/plugins/testdummy/__init__.py

@@ -0,0 +1,17 @@
+from django.apps import AppConfig
+from pretix.base.plugins import PluginType
+
+
+class TestDummyApp(AppConfig):
+    name = 'pretix.plugins.testdummy'
+    verbose_name = '.testdummy'
+
+    class PretixPluginMeta:
+        type = PluginType.RESTRICTION
+        name = '.testdummy'
+        version = '1.0.0'
+
+    def ready(self):
+        from . import signals  # NOQA
+
+default_app_config = 'pretix.plugins.testdummy.TestDummyApp'

src/pretix/plugins/testdummy/signals.py

@@ -0,0 +1,9 @@
+from django.dispatch import receiver
+
+from pretix.base.signals import determine_availability
+
+
+@receiver(determine_availability)
+def availability_handler(sender, **kwargs):
+    kwargs['sender'] = sender
+    return kwargs