  The state-of-the-practice in software development is driven by constant
change fueled by continuous integration servers. Such constant change demands
for frequent and fully automated tests capable to detect faults immediately
upon project build. As the fault detection capability of the test suite becomes
so important, modern software development teams continuously monitor the
quality of the test suite as well. However, it appears that the
state-of-the-practice is reluctant to adopt strong coverage metrics (namely
mutation coverage), instead relying on weaker kinds of coverage (namely branch
coverage). In this paper, we investigate three reasons that prohibit the
adoption of mutation coverage in a continuous integration setting: (1) the
difficulty of its integration into the build system, (2) the perception that
branch coverage is "good enough", and (3) the performance overhead during the
build. Our investigation is based on a case study involving four open source
systems and one industrial system. We demonstrate that mutation coverage
reveals additional weaknesses in the test suite compared to branch coverage and
that it is able to do so with an acceptable performance overhead during project
build.
