
PASS Check the existence of Element.attachShadow 
PASS Nodes other than Element should not have attachShadow 
PASS Element.attachShadow must throw a TypeError if mode is not "open" or "closed" 
PASS Element.attachShadow must create an instance of ShadowRoot 
PASS Element.attachShadow must throw a NotSupportedError if the context object already hosts a shadow tree 
PASS Element.attachShadow must throw a NotSupportedError for non-safelisted elements