The usual way, I think, is known as cross validation. The idea is to break the training set into several parts, known as folds, then select one at a time for assessment and training on the remaining ones.
This, of course, does not measure actual re-equipment or reinforcement, but if you can change the complexity of the model, for example. by changing the regularization term, you can find the optimal point. I think this applies only to training and testing.
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