Context: Automated GUI Exploration Techniques have been widely adopted in the context of mobile apps for supporting critical engineering tasks such as reverse engineering, testing, and network traffic signature generation. Although several techniques have been proposed in the literature, most of them fail to guarantee the exploration of relevant parts of the applications when GUIs require to be exercised with particular and complex input event sequences. We refer to these GUIs as Gate GUIs and to the sequences required to effectively exercise them as Unlocking GUI Input Event Sequences. Objective: In this paper, we aim at proposing a GUI exploration approach that exploits the human involvement in the automated process to solve the limitations introduced by Gate GUIs, without requiring the preliminary configuration of the technique or the user involvement for the entire duration of the exploration process. Method: We propose juGULAR, a Hybrid GUI Exploration Technique combining Automated GUI Exploration with Capture and Replay. Our approach is able to automatically detect Gate GUIs during the app exploration by exploiting a Machine Learning approach and to unlock them by leveraging input event sequences provided by the user. We implement juGULAR in a modular software architecture that targets the Android mobile platform. We evaluate the performance of juGULAR by an experiment involving 14 real Android apps. Results: The experiment shows that the hybridization introduced by juGULAR allows to improve the exploration capabilities in terms of Covered Activities, Covered Lines of Code, and generated Network Traffic Bytes at a reasonable manual intervention cost. The experimental results also prove that juGULAR is able to outperform the state-of-the-practice tool Monkey. Conclusion: We conclude that the combination of Automated GUI Exploration approaches with Capture and Replay techniques is promising to achieve a thorough app exploration. Machine Learning approaches aid to pragmatically integrate these two techniques.
