def __validate(X_test, labels, model, X_scaler):
    """
    Run trained models against validation data
    Arguments:
        X: the test data [n_samples, n_features]
        labels: the GT labels [n_samples, n_classes]
        model: the prediction model
        X_scaler: the standard scaler to scale input features
    Return:
         the mean accuracy on the given test data and labels
    """
    X_test = X_scaler.transform(X_test)
    return model.score(X_test, labels)