Under the widespread of smartphones and tablets, Android devices have gradually become one of the most important elements in our daily life. Along with it, Android applications are now flourishing and their complexity increases geometrically. Meanwhile, Android fragmentation is aggravating, which forces developers to design and develop the same Android apps for different Android versions and devices. In this case, employing models are proposed for requirements and designs in Android app development. With models, dividing and conquering these requirements and designs are possible which reduces the general complexity. At the same time, models of high expression help developers to better understand the purpose and finally guide the development work. However, the traditional models are no longer suitable, since Android apps are even-driven and GUI centric. Therefore, Interaction Flow Modeling Language (IFML) is adopted, the new OMG standard for front-end design and event interaction, in Android app modeling to describe apps' GUI structures and workflows and guide the development. Furthermore, an extension of IFML is proposed for Android to improve its usability and compatibility for Android apps. A formal definition of the IFML model is also given in this paper. The rich semantics of IFML models can elaborate the designs for Android apps, which will further systematically guide the development of these apps during their evolution. Moreover, these IFML models are used to check the consistency between design and implementation in the form of testing. In this way, the effort of writing test cases is reduced and productivity is enhanced as the apps evolve. A tool for modeling and testing for Android apps with IFML is presented, called ADAMANT. To verify the proposed approach's feasibility, ADAMANT is applied on five real-world apps. The results show that the use of the extended IFML in Android app development is effective, and the IFML models can directly be used for testing, ensuring the design is in consistent with the implementation. In this manner, it ensures the quality of development and benefits the sustainable development of apps.