As the soul of the Software-Defined Networking (SDN), the quality of control plane applications determines the reliability of the networks. Unfortunately, better programmability in SDN increases the risk of bugs and challenges for testing. Because manually testing seems to be inefficient, automatic testing methods become promising alternative. Both white-box method with models and black-box method without model have limitations. In this paper, we propose a formal model for blackbox testing of SDN applications. We use a group of components to describe the data structure stored in the applications and the system behaviors. It is easier and more natural to specify applications. Based on our models, we present our work-in-progress testing framework. It can iteratively improve the design model with model verification and expose implement bugs with model-based testing.