tests/stacking: Add test to verify we unmaximize correctly

The test tests that (for both X11 and Wayland) that:

 * The client unmaximizes after mapping maximized to a predictable size
 * That the client unmaximizes to the same size after toggling maximize

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

src/tests/meson.build

@@ -141,6 +141,7 @@ stacking_tests = [
   'override-redirect',
   'set-override-redirect-parent',
   'set-parent-exported',
+  'restore-size',
 ]
 
 foreach stacking_test: stacking_tests

src/tests/stacking/restore-size.metatest

@@ -0,0 +1,53 @@
+# Check that X11 clients restore to their right size after unmaximize
+
+new_client x x11
+create x/1 csd
+
+resize x/1 500 400
+maximize x/1
+show x/1
+
+wait
+
+assert_size x/1 MONITOR_WIDTH MONITOR_HEIGHT
+
+unmaximize x/1
+wait
+
+assert_size x/1 500 400
+
+resize x/1 300 200
+wait
+maximize x/1
+wait_reconfigure
+unmaximize x/1
+wait_reconfigure
+
+assert_size x/1 300 200
+
+# Check that Wayland clients restore to their right size after unmaximize
+
+new_client w wayland
+create w/1 csd
+
+resize w/1 150 300
+maximize w/1
+show w/1
+
+wait
+
+assert_size w/1 MONITOR_WIDTH MONITOR_HEIGHT
+
+unmaximize w/1
+wait_reconfigure
+
+assert_size w/1 150 300
+
+resize w/1 300 200
+wait
+maximize w/1
+wait_reconfigure
+unmaximize w/1
+wait_reconfigure
+
+assert_size w/1 300 200