docs: def register_observer(self):
          """ Register all observable which are of interest
          """
          self.execution_engine.add_observer(self, "start", notify_before_function=self.on_start)
          self.execution_engine.add_observer(self, "pause", notify_before_function=self.on_pause)
          self.execution_engine.add_observer(self, "stop", notify_before_function=self.on_stop)