tests/utils: Add helper for waiting for monitor reconfigurations

This is useful after having removed a virtual monitor, which
will soon reconfigure in an idle callback.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3307>

src/tests/meta-test-utils.c

@@ -780,6 +780,31 @@ meta_set_custom_monitor_config_full (MetaBackend            *backend,
     g_warning ("Failed to set custom config: %s", error->message);
 }
 
+static void
+set_true_cb (gpointer user_data)
+{
+  gboolean *value = user_data;
+
+  *value = TRUE;
+}
+
+void
+meta_wait_for_monitors_changed (MetaContext *context)
+{
+  MetaBackend *backend = meta_context_get_backend (context);
+  MetaMonitorManager *monitor_manager = meta_backend_get_monitor_manager (backend);
+  gulong monitors_changed_handler_id;
+  gboolean monitors_changed = FALSE;
+
+  monitors_changed_handler_id =
+    g_signal_connect_swapped (monitor_manager, "monitors-changed",
+                              G_CALLBACK (set_true_cb), &monitors_changed);
+  while (!monitors_changed)
+    g_main_context_iteration (NULL, TRUE);
+
+  g_signal_handler_disconnect (monitor_manager, monitors_changed_handler_id);
+}
+
 static void
 on_view_presented (ClutterStage      *stage,
                    ClutterStageView  *view,

src/tests/meta-test-utils.h

@@ -114,6 +114,9 @@ void meta_set_custom_monitor_config_full (MetaBackend            *backend,
                                           const char             *filename,
                                           MetaMonitorsConfigFlag  configs_flags);
 
+META_EXPORT
+void meta_wait_for_monitors_changed (MetaContext *context);
+
 META_EXPORT
 void meta_wait_for_paint (MetaContext *context);