public void IsTopLevelValid()
{
var notification = new Notification();
var child = new Notification();
notification.AddChild("something", child);
child.RegisterMessage("f1", "bad", Severity.Error);
notification.IsTopLevelValid().ShouldBeTrue();
notification.RegisterMessage("f2", "not bad", Severity.Warning);
notification.IsTopLevelValid().ShouldBeTrue();
notification.RegisterMessage("f2", "really bad", Severity.Error);
notification.IsTopLevelValid().ShouldBeFalse();
}