double gtk_test_slider_get_value ( GtkWidget* widget )
Retrive the literal adjustment value for GtkRange based
widgets and spin buttons. Note that the value returned by
this function is anything between the lower and upper bounds
of the adjustment belonging to
widget, and is not a percentage
as passed in to gtk_test_slider_set_perc().
This testing infrastructure is phased out in favor of reftests.
Valid widget pointer.
The data is owned by the caller of the function.