gdbus-proxy test: Wait before asserting name owner has gone away

GDBusConnection sends each signal to recipients in a separate idle
callback, and there's no particular guarantee about the order in which
they're scheduled or dispatched. For the NameOwnerChanged signal that
reports the name becoming unowned, it's possible that g_bus_watch_name()
gets its idle callback called before the GDBusProxy:g-name-owner
machinery has updated the name owner, in which case the assertion
will fail.

Fixing GNOME/glib#3268 introduced a new subscription to NameOwnerChanged
which can alter the order of delivery, particularly in the case where
G_DBUS_PROXY_FLAGS_NO_MATCH_RULE was used (as tested in
/gdbus/proxy/no-match-rule). The resulting test failure is intermittent,
but reliably appears within 100 repetitions of that test.

Fixes: 511c5f5b "tests: Wait for gdbus-testserver to die when killing it"
Signed-off-by: Simon McVittie <smcv@debian.org>

gio/tests/gdbus-proxy.c

@@ -780,6 +780,12 @@ kill_test_service (GDBusConnection *connection)
   while (!name_disappeared)
     g_main_context_iteration (NULL, TRUE);
 
+  /* GDBusConnection doesn't guarantee that different subscriptions to the
+   * same signal will get their callbacks scheduled in any particular order,
+   * so make sure they have all happened */
+  while (g_main_context_iteration (NULL, FALSE))
+    continue;
+
   g_bus_unwatch_name (watch_id);
 #else
   g_warning ("Can't kill com.example.TestService");