Fastai-v2 before_validate in callback not doing anything?

fastai fastai dev
1

I’m testing out callbacks in v2, but I noticed that nothing is happening when using before_train or before_validate. When calling learn.fit the below code doesn’t print anything at all, and it keeps training. What am I doing wrong here?

learn = Learner(dls, model, loss_func=mse, cbs=[OnlineEvalCallback])

class OnlineEvalCallback(Callback):
    
    def before_train(self):
        print("before_train")
        
    def before_validate(self):
        print('before_validate')
        
        raise CancelFitException