tests: Ensure MetaX11Display is initialized before running tests

It might not be available right on initialization time if X11 is started
asynchronously. As this is a requirement for our tests, ensure it is there
before proceeding with the test.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/944

src/tests/monitor-unit-tests.c

@@ -343,6 +343,8 @@ create_monitor_test_clients (void)
 {
   GError *error = NULL;
 
+  test_wait_for_x11_display ();
+
   meta_x11_display_set_alarm_filter (meta_get_display ()->x11_display,
                                      monitor_tests_alarm_filter, NULL);
 

src/tests/test-runner.c

@@ -66,6 +66,8 @@ test_case_new (void)
 {
   TestCase *test = g_new0 (TestCase, 1);
 
+  test_wait_for_x11_display ();
+
   meta_x11_display_set_alarm_filter (meta_get_display ()->x11_display,
                                      test_case_alarm_filter, test);
 

src/tests/test-utils.c

@@ -533,3 +533,17 @@ test_get_plugin_name (void)
   else
     return "libdefault";
 }
+
+void
+test_wait_for_x11_display (void)
+{
+  MetaDisplay *display;
+
+  display = meta_get_display ();
+  g_assert_nonnull (display);
+
+  while (!display->x11_display)
+    g_main_context_iteration (NULL, TRUE);
+
+  g_assert_nonnull (display->x11_display);
+}

src/tests/test-utils.h

@@ -84,4 +84,6 @@ void test_client_destroy (TestClient *client);
 
 const char * test_get_plugin_name (void);
 
+void test_wait_for_x11_display (void);
+
 #endif /* TEST_UTILS_H */