public void returns_missing_instance_if_it_exists_and_the_requested_instance_is_not_found()
        {
            var graph = new PluginGraph();
            var family = graph.Families[typeof (IWidget)];
            var missing = new ObjectInstance(new AWidget());
            family.MissingInstance = missing;

            graph.FindInstance(typeof (IWidget), "anything").ShouldBeTheSameAs(missing);
            graph.FindInstance(typeof (IWidget), Guid.NewGuid().ToString()).ShouldBeTheSameAs(missing);
        }