Software testing and Android applications: a large-scale empirical study

These days, over three billion users rely on mobile applications (a.k.a. apps) on a daily basis to access high-speed connectivity and all kinds of services it enables, from social to emergency needs. Having high-quality apps is therefore a vital requirement for developers to keep staying on the market and acquire new users. For this reason, the research community has been devising automated strategies to better test these applications. Despite the effort spent so far, most developers write their test cases manually without the adoption of any tool. Nevertheless, we still observe a lack of knowledge on the quality of these manually written tests: an enhanced understanding of this aspect may provide evidence-based findings on the current status of testing in the wild and point out future research directions to better support the daily activities of mobile developers. We perform a large-scale empirical study targeting 1,693 open-source Android apps and aiming at assessing (1) the extent to which these apps are actually tested, (2) how well-designed are the available tests, (3) what is their effectiveness, and (4) how well manual tests can reduce the risk of having defects in production code. In addition, we conduct a focus group with 5 Android testing experts to discuss the findings achieved and gather insights into the next research avenues to undertake. The key results of our study show Android apps are poorly tested and the available tests have low (i) design quality, (ii) effectiveness, and (iii) ability to find defects in production code. Among the various suggestions, testing experts report the need for improved mechanisms to locate potential defects and deal with the complexity of creating tests that effectively exercise the production code.