Add a test for picker button constructors

This turns out to be hard enough that a test
is useful.

testsuite/gtk/meson.build

@@ -60,6 +60,7 @@ tests = [
   { 'name': 'listlistmodel' },
   { 'name': 'main' },
   { 'name': 'maplistmodel' },
+  { 'name': 'misc' },
   { 'name': 'multiselection' },
   { 'name': 'noselection' },
   { 'name': 'notify' },

testsuite/gtk/misc.c

@@ -0,0 +1,50 @@
+/* Copyright (C) 2022 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <gtk/gtk.h>
+
+static void
+test_color_dialog_button_new (void)
+{
+  GtkWidget *button;
+
+  /* check that the constructor accepts NULL */
+  button = gtk_color_dialog_button_new (NULL);
+  g_object_ref_sink (button);
+  g_object_unref (button);
+}
+
+static void
+test_font_dialog_button_new (void)
+{
+  GtkWidget *button;
+
+  /* check that the constructor accepts NULL */
+  button = gtk_color_dialog_button_new (NULL);
+  g_object_ref_sink (button);
+  g_object_unref (button);
+}
+
+int
+main (int   argc,
+      char *argv[])
+{
+  gtk_test_init (&argc, &argv);
+
+  g_test_add_func ("/colordialogbutton/new", test_color_dialog_button_new);
+  g_test_add_func ("/fontdialogbutton/new", test_font_dialog_button_new);
+
+  return g_test_run();
+}