  Background. Evidence suggests that mobile applications are not thoroughly
tested as their desktop counterparts. In particular GUI testing is generally
limited. Like web-based applications, mobile apps suffer from GUI test
fragility, i.e. GUI test classes failing due to minor modifications in the GUI,
without the application functionalities being altered.
  Aims. The objective of our study is to examine the diffusion of GUI testing
on Android, and the amount of changes required to keep test classes up to date,
and in particular the changes due to GUI test fragility. We define metrics to
characterize the modifications and evolution of test classes and test methods,
and proxies to estimate fragility-induced changes.
  Method. To perform our experiments, we selected six widely used open-source
tools for scripted GUI testing of mobile applications previously described in
the literature. We have mined the repositories on GitHub that used those tools,
and computed our set of metrics.
  Results. We found that none of the considered GUI testing frameworks achieved
a major diffusion among the open-source Android projects available on GitHub.
For projects with GUI tests, we found that test suites have to be modified
often, specifically 5\%-10\% of developers' modified LOCs belong to tests, and
that a relevant portion (60\% on average) of such modifications are induced by
fragility.
  Conclusions. Fragility of GUI test classes constitute a relevant concern,
possibly being an obstacle for developers to adopt automated scripted GUI
tests. This first evaluation and measure of fragility of Android scripted GUI
testing can constitute a benchmark for developers, and the basis for the
definition of a taxonomy of fragility causes, and actionable guidelines to
mitigate the issue.
