Stop using xvfb-run in tests

Except the X11 backend test, it still needs an X server. Eventually we
can replace it with the equivalent that uses Xwayland, but that needs a
"scaled down" mutter that runs as the host compositor for Xwayland, that
doesn't expose anything on the session bus.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3812>

.gitlab-ci.yml

@@ -516,8 +516,8 @@ build-wayland-only@x86_64:
     - .test-mutter-base
   script:
     - glib-compile-schemas $GSETTINGS_SCHEMA_DIR
-    - xvfb-run -a -s "$XVFB_SERVER_ARGS"
-        ./src/tests/meta-dbus-runner.py
+    - mkdir -m 1777 /tmp/.X11-unix
+    - ./src/tests/meta-dbus-runner.py
         --launch=pipewire
         --launch=wireplumber
         --
@@ -614,7 +614,8 @@ can-run-gnome-shell@x86_64:
     - .gitlab-ci/checkout-gnome-shell.sh
     - meson setup gnome-shell gnome-shell/build --prefix /usr -Dbuildtype=debugoptimized -Dman=false --werror --fatal-meson-warnings
     - sudo meson install -C gnome-shell/build
-    - dbus-run-session -- xvfb-run meson test -C gnome-shell/build --no-rebuild --timeout-multiplier 5
+    - mkdir -m 1777 /tmp/.X11-unix
+    - dbus-run-session -- meson test -C gnome-shell/build --no-rebuild --timeout-multiplier 5
   artifacts:
     expire_in: 7 day
     name: "mutter-${CI_JOB_NAME}-${CI_COMMIT_REF_NAME}"
@@ -685,8 +686,8 @@ dist-mutter:
     - meson setup . build --werror --prefix /usr
         -Dbuildtype=debugoptimized
     - glib-compile-schemas $GSETTINGS_SCHEMA_DIR
-    - xvfb-run -a -s "$XVFB_SERVER_ARGS"
-        ./src/tests/meta-dbus-runner.py
+    - mkdir -m 1777 /tmp/.X11-unix
+    - ./src/tests/meta-dbus-runner.py
         --launch=pipewire
         --launch=wireplumber
         --

doc/debugging.md

@@ -92,11 +92,9 @@ Renderdoc is usually the better tool to debug something with, but it's also hard
     ```sh
     export XDG_RUNTIME_DIR=$PWD/runtime-dir
     mkdir -p $XDG_RUNTIME_DIR
-    ./src/tests/meta-dbus-runner.py xvfb-run meson test -C build --setup plain --gdb failing-test-case
+    ./src/tests/meta-dbus-runner.py meson test -C build --setup plain --gdb failing-test-case
     ```
 
-    The need for `xvfb-run` depends on whether the test case uses the nested backend or the headless backend.
-
     If it involves screen casting, it becomes a bit more complicated:
 
     ```sh

meson.build

@@ -351,6 +351,7 @@ have_native_tests = false
 have_kvm_tests = false
 have_tty_tests = false
 have_installed_tests = false
+have_x11_tests = false
 
 if have_tests
   gtk3_dep = dependency('gtk+-3.0', version: gtk3_req)
@@ -417,13 +418,12 @@ if have_tests
 
   add_test_setup('plain')
 
-  xvfb = find_program('xvfb-run')
-  xvfb_args = [
-    '-a',
-    '-s',
-    '+iglx -noreset',
-  ]
-  xvfb_command = [xvfb] + xvfb_args
+  if have_x11
+    xvfb = find_program('xvfb-run', required: false)
+    if xvfb.found()
+      have_x11_tests = true
+    endif
+  endif
 
   add_test_setup('CI',
     env: [
@@ -431,7 +431,6 @@ if have_tests
     ],
     exe_wrapper: [
       default_test_wrappers,
-      xvfb_command,
     ],
     timeout_multiplier: 10,
   )
@@ -759,5 +758,6 @@ summary('Core tests', have_core_tests, section: 'Tests')
 summary('Cogl tests', have_cogl_tests, section: 'Tests')
 summary('Clutter tests', have_clutter_tests, section: 'Tests')
 summary('KVM tests', get_option('kvm_tests'), section: 'Tests')
+summary('X11 backend', have_x11_tests, section: 'Tests')
 summary('Installed tests', have_installed_tests, section: 'Tests')
 summary('Coverage', get_option('b_coverage'), section: 'Tests')

src/tests/meson.build

@@ -828,7 +828,13 @@ if have_kvm_tests or have_tty_tests
   endif
 endif
 
-if have_x11
+if have_x11_tests
+  xvfb_args = [
+    '-a',
+    '-s',
+    '+iglx -noreset',
+  ]
+
   foreach mode: ['', 'sync']
     x11_env = test_env
     if mode == 'sync'

src/tests/stacking.test.in

@@ -4,6 +4,6 @@ Description=Mutter stacking test: @stacking_test@
 # a solution for
 # https://gitlab.gnome.org/GNOME/gnome-desktop-testing/-/issues/1,
 # and anyway that wouldn't be sufficient to handle XDG_RUNTIME_DIR
-Exec=sh -ec 'env GSETTINGS_BACKEND=memory XDG_CURRENT_DESKTOP= XDG_RUNTIME_DIR="$(mktemp -d -t mutter-@apiversion@-@stacking_test@-XXXXXX)" @libexecdir@/installed-tests/mutter-@apiversion@/mutter-installed-dbus-session.py xvfb-run -a -s "+iglx -noreset" -- @libexecdir@/installed-tests/mutter-@apiversion@/mutter-test-runner @tests_datadir@/stacking/@stacking_test@.metatest'
+Exec=sh -ec 'env GSETTINGS_BACKEND=memory XDG_CURRENT_DESKTOP= XDG_RUNTIME_DIR="$(mktemp -d -t mutter-@apiversion@-@stacking_test@-XXXXXX)" @libexecdir@/installed-tests/mutter-@apiversion@/mutter-installed-dbus-session.py -- @libexecdir@/installed-tests/mutter-@apiversion@/mutter-test-runner @tests_datadir@/stacking/@stacking_test@.metatest'
 Type=session
 Output=TAP