GSettings overrides can be active and set the default value depending on
the XDG_CURRENT_DESKTOP environement variable. For the tests we run, we
rely on the default settings by using the GSettings memory backend but
we also need to make sure not overrides are in place.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3730>
Running each stacking test as a separate installed-test is analogous to
what was done for build-time tests in c6d1cf4a (!442) and should make it
easier to track regressions, by being able to see whether a regression
is specific to one .metatest script or applies to more than one.
Signed-off-by: Simon McVittie <smcv@debian.org>
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2773>
