in src/DeloitteDigital.Atlas/Extensions/ItemExtensions.cs [216:235]
public static bool InheritsFromTemplate(this Item item, ID id)
{
if (item == null || StandardValuesManager.IsStandardValuesHolder(item)) return false;
// Check if it is directly inheriting
if (item.TemplateID == id) return true;
// Else check the base templates.
var template = Sitecore.Data.Managers.TemplateManager.GetTemplate(item);
if (template == null) return false;
foreach (Template template2 in template.GetBaseTemplates())
{
if (template2 == null) continue;
if (template2.ID.Guid == id.Guid) return true;
}
return false;
}