By their very nature, services are accessible only as black-boxes through their published interfaces. It is a well known issue that lack of implementation details may reduce service testability. In previous work, we proposed testable services as a solution to provide third-party services with structural coverage information after a test session, yet without revealing their internal details. However, integrators do not have enough information to improve their test set when they get a low coverage measure because they do not know which test requirements have not been covered. This paper proposes an approach in which testable services are provided along with test metadata that may help integrators to get a higher coverage. The approach is illustrated on a case study of a real system that uses orchestrations and testable services. A formal experiment designed to compare the proposed solution with a functional approach is also presented. The results show evidences that subjects using the testable service approach augmented with metadata can achieve better coverage than subjects using only a functional approach.