tests/stacking: Alt+Tab focus+stacking test for globally active input

Gnome-shell uses meta_display_focus_default_window() when shell elements
loose focus which is the case with Alt+Tab window switching. Globally
active input clients don't immediately gain focus though so if
meta_display_focus_default_window focuses a wrong window stacking and
focus don't behave as expected.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2489>

src/tests/meson.build

@@ -443,6 +443,7 @@ stacking_tests = [
   'workspace-basic',
   'workspace-test',
   'always-on-top',
+  'focus-default-window-globally-active-input',
 ]
 
 foreach stacking_test: stacking_tests

src/tests/stacking/focus-default-window-globally-active-input.metatest

@@ -0,0 +1,20 @@
+new_client 0 x11
+create 0/1
+accept_focus 0/1 false
+can_take_focus 0/1 true
+accept_take_focus 0/1 true
+show 0/1
+
+new_client 1 wayland
+create 1/1
+show 1/1
+
+assert_stacking 0/1 1/1
+assert_focused 1/1
+
+local_activate 0/1
+focus_default_window
+
+wait
+assert_stacking 1/1 0/1
+assert_focused 0/1

src/tests/test-runner.c

@@ -1171,6 +1171,16 @@ test_case_do (TestCase *test,
       else
         meta_window_unmake_above (window);
     }
+  else if (strcmp (argv[0], "focus_default_window") == 0)
+    {
+      if (argc != 1)
+        BAD_COMMAND("usage: %s", argv[0]);
+
+      MetaDisplay *display = meta_get_display ();
+      uint32_t timestamp = meta_display_get_current_time_roundtrip (display);
+
+      meta_display_focus_default_window (display, timestamp);
+    }
   else
     {
       BAD_COMMAND("Unknown command %s", argv[0]);