  
          apps.lazy_model_operation(dummy_function, ('auth', 'imaginarymodel'))
          apps.lazy_model_operation(dummy_function, ('fanciful_app', 'imaginarymodel'))
  
          errors = _check_lazy_references(apps)
  
          expected = [
              Error(
                  "%r contains a lazy reference to auth.imaginarymodel, "
                  "but app 'auth' doesn't provide model 'imaginarymodel'." % dummy_function,
 
</s> remove         msg = "Specified sender must either be a model or a model name of the 'app_label.ModelName' form."
 </s> add         msg = "Invalid model reference 'invalid'. String model references must be of the form 'app_label.ModelName'." </s> remove             self.receiver, sender='signals.Created', weak=False
 </s> add             self.receiver, sender='signals.Created', weak=False, apps=apps
        post_init.connect(dummy_function, sender='missing-app.Model', apps=apps)
        post_init.connect(DummyClass(), sender='missing-app.Model', apps=apps)
        post_init.connect(DummyClass().dummy_method, sender='missing-app.Model', apps=apps)
  
          apps.lazy_model_operation(dummy_function, ('auth', 'imaginarymodel'))
          apps.lazy_model_operation(dummy_function, ('fanciful_app', 'imaginarymodel'))
  
        post_init.connect(dummy_function, sender='missing-app.Model', apps=apps)
        post_init.connect(DummyClass(), sender='missing-app.Model', apps=apps)
        post_init.connect(DummyClass().dummy_method, sender='missing-app.Model', apps=apps)
  
          expected = [
              Error(
                  "%r contains a lazy reference to auth.imaginarymodel, "
                  "but app 'auth' doesn't provide model 'imaginarymodel'." % dummy_function,
keep keep keep keep replace keep keep keep keep keep
 Fixed #26421 -- Refactored ModelSignal to use Apps.lazy_model_operation() 
tests/model_validation/tests.py