Clear listeners in the global notifier instance at the start of simulation

Author: tamuri

src/tlo/notify.py

@@ -60,6 +60,13 @@ def dispatch(self, notification_key, data=None):
             for listener in self.listeners[notification_key]:
                 listener(data)
 
+    def clear_listeners(self):
+        """
+        Clear all registered listeners. Essential because the notifier is a global singleton.
+        e.g. if you are running multiple tests or simulations in the same process.
+        """
+        self.listeners.clear()
+
 
 # Create a global notifier instance
 notifier = Notifier()

src/tlo/simulation.py

@@ -26,6 +26,7 @@
     topologically_sort_modules,
 )
 from tlo.events import Event, IndividualScopeEventMixin
+from tlo.notify import notifier
 from tlo.progressbar import ProgressBar
 
 if TYPE_CHECKING:
@@ -116,6 +117,8 @@ def __init__(
         self._custom_log_levels = None
         self._log_filepath = self._configure_logging(**log_config)
 
+        # clear notifier listeners from any previous simulation in this process
+        notifier.clear_listeners()
 
         # random number generator
         seed_from = "auto" if seed is None else "user"