Code review comment for lp:~jamesh/thumbnailer/no-fallback-albumart

So, the QML tests are already setting XDG_CACHE_HOME.

I was having some trouble with those tests failing locally while passing in Jenkins, which I think I have solved since you made your original comment. In my environment I had QT_QPA_PLATFORMTHEME=appmenu-qt5, which seemed to be initialising the D-Bus connection prior to me replacing it with libqtdbustest. This meant the test was running against the installed copy of thumbnailer-service.

With the updates in the branch, ctest will blank out this environment variable when running the test, which made those tests pass reliably for me.