Debugging widgets

Hi, 

I am trying to understand how to debug a widget. I am trying to do
something like this. This is just a test.

	Gtk::Box box;
	BOOST_TEST(box.get_homogeneous() == true);

I get the following error:

(process:25274): Gtk-CRITICAL **: 14:36:20.149:
_gtk_css_lookup_resolve: assertion '(((__extension__ ({ GTypeInstance
*__inst = (GTypeInstance*) ((provider)); GType __t =
((_gtk_style_provider_private_get_type ())); gboolean __r; if (!__inst)
__r = (0); else if (__inst->g_class && __inst->g_class->g_type == __t)
__r = (!(0)); else __r = g_type_check_instance_is_a (__inst, __t); __r;
}))))' failed

(process:25274): GLib-GObject-CRITICAL **: 14:36:20.149:
g_object_set_data_full: assertion 'G_IS_OBJECT (object)' failed

(process:25274): Gtk-ERROR **: 14:36:20.149: ../../checkout/gtk+-
3/gtk/gtkstylecontext.c:348:gtk_style_context_init: Can't create a
GtkStyleContext without a display connection

Since Gtk::Box is not a top level widget is has no CSS styles
associated with it. What would be the best practice to add CSS styles
(ctor?) and eventually, how to debug a widget? I assume, we don't need
to call any show() methods. 

Thanks.
-Pavlo