Move testdummy plugin to the test directory

src/tests/testdummy/signals.py

@@ -0,0 +1,15 @@
+from django.dispatch import receiver
+
+from pretix.base.signals import determine_availability
+
+
+@receiver(determine_availability)
+def availability_handler(sender, **kwargs):
+    kwargs['sender'] = sender
+    if sender.settings.testdummy_available is not None:
+        variations = kwargs['variations']
+        variations = [d.copy() for d in variations]
+        for v in variations:
+            v['available'] = (sender.settings.testdummy_available == 'yes')
+        return variations
+    return []