A Rounded Evaluation of Recommender Systems
EvalRS: Evaluating Recommender Systems on Many Tests
Recommender Systems are probably one of the most popular machine learning systems in production; moreover, recommenders are probably the machine learning products that have the closest contact with the actual users, since they are generally used in an interactive fashion.
This is why testing is fundamental in Recommender Systems. Failing to detect low performance in some cases can bring reputational damage to a company.