The mutter tests require to run in a valid environment where a display
is available and a session bus, however currently we rely on the current
environment, and this may lead to unexpected behaviors.
So let's just ensure that a display is running through xvfb-run and
that a session bus is running in a temporary directory.
We also ensure to use the gsettings memory backend, even because by
setting TestEnvironment we ensure that no other env variable is leaked
to the test.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1876>
This is the last remaining feature necessary to achieve
parity with the Autotools build.
A few changes were made to the install locations of the
tests, in order to better acomodate them in Meson:
* Tests are now installed under a versioned folder (e.g.
/usr/share/installed-tests/mutter-4)
* The mutter-cogl.test file is now generated from an .in
file, instead of a series of $(echo)s from within Makefile.
Notice that those tests need very controlled environments
to run correctly. Mutter installed tests, for example, will
failed when running under a regular session due to D-Bus
failing to acquire the ScreenCast and/or RemoteScreen names.
