tests: Add basic X11 WM test

This launches Xvfb, using xvfb-run, and inside tests the following:

  1. Launching 'mutter --x11' works
  2. Launching a couple of X11 clients works (doesn't crash or result in
     warnings)
  3. Launching 'mutter --x11 --replace' works
  4. Terminating works

It does this using a simple shell script.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2434>

src/tests/meson.build

@@ -409,3 +409,18 @@ if have_kvm_tests or have_tty_tests
     endforeach
   endif
 endif
+
+if have_x11
+  test('x11', xvfb,
+    args: [
+      xvfb_args,
+      find_program('x11-test.sh').full_path(),
+      mutter.full_path(),
+    ],
+    depends: [mutter],
+    suite: ['core', 'mutter/x11'],
+    env: test_env,
+    is_parallel: false,
+    timeout: 60,
+  )
+endif

src/tests/x11-test.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/bash
+
+set -e
+
+MUTTER="$1"
+
+if [ -z "$MUTTER" ]; then
+  echo Usage: $0 PATH-TO-MUTTER > /dev/stderr
+  exit 1
+fi
+
+export GDK_BACKEND=x11
+export G_DEBUG=fatal-warnings
+
+echo \# Launching mutter > /dev/stderr
+$MUTTER --x11 --mutter-plugin="$MUTTER_TEST_PLUGIN_PATH" &
+MUTTER1_PID=$!
+gdbus wait --session org.gnome.Mutter.IdleMonitor
+echo \# Launched with pid $MUTTER1_PID
+
+sleep 2
+
+echo Launching a couple of X11 clients > /dev/stderr
+zenity --warning &
+ZENITY1_PID=$!
+sleep 2
+zenity --info &
+ZENITY2_PID=$!
+sleep 4
+
+echo \# Replacing existing mutter with a new instance > /dev/stderr
+$MUTTER --x11 --replace --mutter-plugin="$MUTTER_TEST_PLUGIN_PATH" &
+echo \# Launched with pid $MUTTER2_PID
+MUTTER2_PID=$!
+wait $MUTTER1_PID
+
+sleep 2
+
+echo \# Terminating clients > /dev/stderr
+kill $ZENITY1_PID
+sleep 1
+kill $ZENITY2_PID
+sleep 1
+
+echo \# Terminating mutter > /dev/stderr
+kill $MUTTER2_PID
+wait $MUTTER2_PID