test: test the "append to events settings" functionality

and fix coverage

event_routing_backends/settings/common.py

@@ -205,6 +205,8 @@ def plugin_settings(settings):
         settings.EVENT_TRACKING_BACKENDS_ALLOWED_CALIPER_EVENTS
     )
 
+    if not hasattr(settings, 'EVENT_TRACKING_BACKENDS') or not settings.EVENT_TRACKING_BACKENDS:
+        settings.EVENT_TRACKING_BACKENDS = {}
     settings.EVENT_TRACKING_BACKENDS.update(event_tracking_backends_config(
         settings,
         settings.EVENT_TRACKING_BACKENDS_ALLOWED_XAPI_EVENTS,

event_routing_backends/tests/test_settings.py

@@ -3,7 +3,7 @@
 """
 
 from django.conf import settings
-from django.test import TestCase
+from django.test import override_settings, TestCase
 
 from event_routing_backends.settings import common as common_settings
 from event_routing_backends.settings import devstack as devstack_settings
@@ -82,3 +82,17 @@ def test_production_settings(self):
         self.assertTrue(settings.CALIPER_EVENT_LOGGING_ENABLED)
         self.assertFalse(settings.XAPI_EVENTS_ENABLED)
         self.assertTrue(settings.XAPI_EVENT_LOGGING_ENABLED)
+
+    @override_settings(
+        EVENT_TRACKING_BACKENDS_ALLOWED_XAPI_EVENTS=["my.event.1"],
+        EVENT_TRACKING_BACKENDS_ALLOWED_CALIPER_EVENTS=["my.event.2"],
+        EVENT_TRACKING_BACKENDS={},
+    )
+    def test_settings_append_events(self):
+        common_settings.plugin_settings(settings)
+
+        self.assertGreater(len(settings.EVENT_TRACKING_BACKENDS_ALLOWED_XAPI_EVENTS), 1)
+        self.assertIn("my.event.1", settings.EVENT_TRACKING_BACKENDS_ALLOWED_XAPI_EVENTS)
+
+        self.assertGreater(len(settings.EVENT_TRACKING_BACKENDS_ALLOWED_CALIPER_EVENTS), 1)
+        self.assertIn("my.event.2", settings.EVENT_TRACKING_BACKENDS_ALLOWED_CALIPER_EVENTS)