Done with getting the OS X build to succeed again on Travis-CI. In the end, the issue was that our new tests strategy requires deploying (and cleaning up) various Qt plugins. Now, the problem when installing Qt 5 with brew, the resulting Qt 5 files had a 444 right accesses, which means that we couldn't clean them, etc. So, the solution was simply to change their right accesses to 755, but I hadn't realised that /usr/local/opt/qt5 is actually a symbolic link, so we can't change right accesses on it and instead we need to change them on /usr/local/opt/qt5/*. From there, everything's fine!