[mutter] tests/stacking: Add test for when no default focus window can be found

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit d85c3c1e940a6f42a4f38cf3ad9f8768a90485df
Author: Sebastian Keller <skeller gnome org>
Date:   Fri Jun 26 21:32:39 2020 +0200

    tests/stacking: Add test for when no default focus window can be found
    
    The previous commit removed checks for intermediate focus states which
    would make tests randomly fail, because of their time dependence. What
    can be tested however is that if there is no other window available that
    would accept the focus, that the focus remains at 'none', after the
    focused window has been closed. This newly introduced test checks the
    focus directly after closing the window (and syncing) and after the time
    it would have taken for the queue to finish. The first check has a
    similar timing issue as the removed focus checks in the other tests, but
    the test will never accidentally fail, because regardless of whether the
    queue has finished or not, the focus is always expected to be 'none'.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1329

 src/tests/meson.build                              |  1 +
 .../closed-transient-no-default-focus.metatest     | 29 ++++++++++++++++++++++
 2 files changed, 30 insertions(+)
---
diff --git a/src/tests/meson.build b/src/tests/meson.build
index 92d110375e..77ab3b5d6d 100644
--- a/src/tests/meson.build
+++ b/src/tests/meson.build
@@ -149,6 +149,7 @@ stacking_tests = [
   'basic-wayland',
   'client-side-decorated',
   'closed-transient',
+  'closed-transient-no-default-focus',
   'closed-transient-no-input-no-take-focus-parent',
   'closed-transient-no-input-no-take-focus-parents',
   'closed-transient-no-input-parent',
diff --git a/src/tests/stacking/closed-transient-no-default-focus.metatest 
b/src/tests/stacking/closed-transient-no-default-focus.metatest
new file mode 100644
index 0000000000..a2db12d5ba
--- /dev/null
+++ b/src/tests/stacking/closed-transient-no-default-focus.metatest
@@ -0,0 +1,29 @@
+new_client 1 x11
+create 1/1
+accept_focus 1/1 false
+show 1/1
+
+create 1/2 csd
+set_parent 1/2 1
+accept_focus 1/2 false
+show 1/2
+
+create 1/3 csd
+set_parent 1/3 2
+show 1/3
+
+wait
+assert_focused 1/3
+assert_stacking 1/1 1/2 1/3
+
+destroy 1/3
+wait
+
+assert_focused none
+assert_stacking 1/1 1/2
+
+sleep 150
+wait
+
+assert_focused none
+assert_stacking 1/1 1/2