Unit testing is a fundamental activity of software quality assurance. As it needs extra knowledge and effort than just programming skill, it may not be well carried out or even be completely ignored. The paper proposes a testing model-Testing as a Service (TaaS), which provides unit testing services to partake the burden of programmers. Bringing TaaS into effect faces a lot of challenges. We put forward to use Ontology technique to model testing knowledge and use SWRL (Semantic Web Rules Language) to describe matching rules between tenant test requests and TaaS capability. Test Service Bus (TSB) is built to recognize the semantics of test requests, map to corresponding test capability based on automatic inference, choreograph testing servic...