Need some help writing mock tests implementation for surface controllers. Unable to mock IPublishedContent methods in Umbraco *

I initially tried to Mock IPublishedContent as mentioned below.

 Mock<IPublishedContent> mockIdentifierTypeContent = new Mock<IPublishedContent>();
SiteSettings siteSettings = Umbraco.Content(request.HomePageId) as SiteSettings;

and able to successfully mock content in SiteSettings object.

but looking to mock the SiteSettings Descendants as mentioned in the line below.

siteSettings.Descendants<Registration>().FirstOrDefault(s => s.Id == request.PageId);


 public static IEnumerable<T> Descendants<T>(this IPublishedContent content, string culture = null)
            where T : class, IPublishedContent
        {
            return content.Descendants(culture).OfType<T>();
        }

Any inputs or Suggestions greatly appreciated. Thanks in advance.