Testing LightBox dialogs (SharePoint)

Try using the VisibleOnScreen property to check this. Another option is object size properties - invisible items often have zero size. Also, Sharepoint applications are usual web applications as far as I know, so you can consider checking runtime CSS styles to find out whether an element is supposed to be visible. The CSS properties to check are "display" ("none" for invisible items), "visibility" ("hidden" for hidden items), "width" and "height" (can be zero for hidden items) depending on how items are "cleared from view" in your specific application. Please see the "Getting CSS Attributes" article for more information.