  Fragile (i.e., non-robust) test execution is a common challenge for automated
GUI-based testing of web applications as they evolve. Despite recent progress,
there is still room for improvement since test execution failures caused by
technical limitations result in unnecessary maintenance costs that limit its
effectiveness and efficiency. One of the most reported technical challenges for
web-based tests concerns how to reliably locate a web element used by a test
script. This paper proposes the novel concept of Visually Overlapping Nodes
(VON) that reduces fragility by utilizing the phenomenon that visual web
elements (observed by the user) are constructed from multiple web-elements in
the Document Object Model (DOM) that overlaps visually. We demonstrate the
approach in a tool, VON Similo, which extends the state-of-the-art
multi-locator approach (Similo) that is also used as the baseline for an
experiment. In the experiment, a ground truth set of 1163 manually collected
web element pairs, from different releases of the 40 most popular websites on
the internet, are used to compare the approaches' precision, recall, and
accuracy. Our results show that VON Similo provides 94.7% accuracy in
identifying a web element in a new release of the same SUT. In comparison,
Similo provides 83.8% accuracy. These results demonstrate the applicability of
the visually overlapping nodes concept/tool for web element localization in
evolving web applications and contribute a novel way of thinking about web
element localization in future research on GUI-based testing.
