code: def update(self, event, instance):
      self.counter += 1
  
file_path: BayesianOptimization/tests/test_observer.py
imports: from bayes_opt.bayesian_optimization import Observable
  from bayes_opt.observer import _Tracker
  from bayes_opt.event import Events
  import os
label_desc: Use image node_id 2 for calling the SimpleObserver obj's underlying member method code with example usage: obj.update(event, instance) without return types