Update warning when invalid delivery is set

bugsnag/configuration.py

@@ -271,7 +271,20 @@ def delivery(self):
 
     @delivery.setter  # type: ignore
     def delivery(self, value):
-        if hasattr(value, 'deliver') and callable(value.deliver):
+        has_deliver = hasattr(value, 'deliver') and callable(value.deliver)
+        has_deliver_sessions = hasattr(value, 'deliver_sessions') and callable(value.deliver_sessions)
+
+        if has_deliver and has_deliver_sessions:
+            has_options_parameter = 'options' in value.deliver_sessions.__code__.co_varnames
+
+            if not has_options_parameter:
+                warnings.warn(
+                    'delivery.deliver_sessions should accept an "options" ' +
+                    'parameter to allow for synchronous delivery, sessions' +
+                    'sessions may be lost when the process exits',
+                    DeprecationWarning
+                )
+
             self._delivery = value
         else:
             message = ('delivery should implement Delivery interface, got ' +