tests/stacking: Check that unmaximize to new size works

A client that set a new fallback size while being maximized should not
restore to the one prior to being maximized.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1171

src/tests/meson.build

@@ -142,6 +142,7 @@ stacking_tests = [
   'set-override-redirect-parent',
   'set-parent-exported',
   'restore-size',
+  'unmaximize-new-size',
 ]
 
 foreach stacking_test: stacking_tests

src/tests/stacking/unmaximize-new-size.metatest

@@ -0,0 +1,22 @@
+# This is only tested on Wayland since it's broken on X11
+
+new_client w wayland
+create w/1 csd
+
+resize w/1 500 400
+show w/1
+wait
+
+assert_size w/1 500 400
+
+maximize w/1
+wait_reconfigure
+assert_size w/1 MONITOR_WIDTH MONITOR_HEIGHT
+
+resize w/1 300 500
+wait_reconfigure
+assert_size w/1 MONITOR_WIDTH MONITOR_HEIGHT
+
+unmaximize w/1
+wait_reconfigure
+assert_size w/1 300 500