How does catboost convert categorical features in test dataset to numeric features

Based on the article on catboost website (https://tech.yandex.com/catboost/doc/dg/concepts/algorithm-main-stages_cat-to-numberic-docpage/), the catboost uses the response to convert categorical feature to numerical features. I can understand that it works for training data with response, but I am wondering how it works for prediction that does not have responses.

Thanks