Mobile GUI Testing Fragility: A Study on Open-Source Android Applications

Android applications do not seem to be tested as thoroughly as desktop ones. In particular, graphical user interface (GUI) testing appears generally limited. Like web-based applications, mobile apps suffer from GUI test fragility, i.e., GUI test classes failing or needing updates due to even minor modifications in the GUI or in the application under test. The objective of our study is to estimate the adoption of GUI testing frameworks among Android open-source applications, the quantity of modifications needed to keep test classes up to date, and their amount due to GUI test fragility. We introduce a set of 21 metrics to measure the adoption of testing tools and the evolution of test classes and test methods, and to estimate the fragility of test suites. We computed our metrics for six GUI testing frameworks, none of which achieved a significant adoption among Android projects hosted on GitHub. When present, GUI test methods associated with the considered tools are modified often, and a relevant portion (70% on average) of those modifications is induced by GUI-related fragilities. On average, for the projects considered, more than 7% of the total modified lines of code between consecutive releases belong to test classes developed with the analyzed testing frameworks. The measured percentage was higher on average than the one required by other generic test code, based on the JUnit testing framework. Fragility of GUI tests constitutes a relevant concern, probably an obstacle for developers to adopt test automation. This first evaluation of the fragility of Android scripted GUI testing can constitute a benchmark for developers and testers leveraging the analyzed test tools and the basis for the definition of a taxonomy of fragility causes and guidelines to mitigate the issue.