tests: Add test for unfullscreening followed by immediate strut change

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2066>

src/tests/meson.build

@@ -288,6 +288,7 @@ stacking_tests = [
   'restore-size',
   'unmaximize-new-size',
   'fullscreen-maximize',
+  'unfullscreen-strut-change',
   'restore-position',
   'default-size',
   'modals',

src/tests/stacking/unfullscreen-strut-change.metatest

@@ -0,0 +1,49 @@
+# Tests that the following works, both on Wayland and X11
+#  1. Create a window with a known size
+#  2. Fullscreen window results in fullscreen size
+#  3. Unfullscreen window followed by a strut change returns to known size
+
+new_client w wayland
+create w/1 csd
+
+resize w/1 500 400
+show w/1
+wait
+
+assert_size w/1 500 400
+
+fullscreen w/1
+wait_reconfigure
+assert_size w/1 MONITOR_WIDTH MONITOR_HEIGHT
+
+stop_after_next w
+unfullscreen w/1
+wait
+set_strut 0 0 1 1 top
+continue w
+wait_reconfigure
+assert_size w/1 500 400
+
+clear_struts
+wait
+
+new_client x x11
+create x/1 csd
+
+resize x/1 500 400
+show x/1
+wait
+
+assert_size x/1 500 400
+
+fullscreen x/1
+wait_reconfigure
+assert_size x/1 MONITOR_WIDTH MONITOR_HEIGHT
+
+stop_after_next x
+unfullscreen x/1
+wait
+set_strut 0 0 1 1 top
+continue x
+wait_reconfigure
+assert_size x/1 500 400