Code coverage-based regression test selection and prioritization in WebKit

Automated regression testing is often crucial in order to maintain the quality of a continuously evolving software system. However, in many cases regression test suites tend to grow too large to be suitable for full re-execution at each change of the software. In this case selective retesting can be applied to reduce the testing cost while maintaining similar defect detection capability. One of the basic test selection methods is the one based on code coverage information, where only those tests are included that cover some parts of the changes. We experimentally applied this method to the open source web browser engine project WebKit to find out the technical difficulties and the expected benefits if this method is to be introduced into the actual build process. Although the principle is simple, we had to solve a number of technical issues, so we report how this method was adapted to be used in the official build environment. Second, we present results about the selection capabilities for a selected set of revisions of WebKit, which are promising. We also applied different test case prioritization strategies to further reduce the number of tests to execute. We explain these strategies and compare their usefulness in terms of defect detection and test suite reduction.