add tests, fix bug in legacy name splitting

src/pretix/base/datasync/sourcefields.py

@@ -492,7 +492,7 @@ def get_data_fields(event, for_model=None):
                 _("Attendee") + ": " + _("Family name") + " (⚠️ auto-generated, not recommended)",
                 Question.TYPE_STRING,
                 None,
-                lambda position: split_name_on_last_space(position.attendee_name.rsplit, part=1),
+                lambda position: split_name_on_last_space(position.attendee_name, part=1),
                 deprecated=True,
             ),
             DataFieldInfo(

src/pretix/base/signals.py

@@ -257,8 +257,14 @@ class Registry:
                      When a new entry is registered, all accessor functions are called with the new entry as parameter.
                      Their return value is stored as the metadata value for that key.
         """
-        self.registered_entries = dict()
         self.keys = keys
+        self.clear()
+
+    def clear(self):
+        """
+        Removes all entries from the registry.
+        """
+        self.registered_entries = dict()
         self.by_key = {key: {} for key in self.keys.keys()}
 
     def register(self, *objs):