Test cases for exists

SPARQL 1.1 Query Language Grammar enables  "exists" pattern in several 
interesting places, in particular:

select ( exists{?x ex:name 'J.Doe'} as ?b) where

group by exists {?x ex:name 'J.Doe'}

order by exists {?x ex:name 'J.Doe'}

having exists {?x ex:name 'J.Doe'}


It may be useful to include test cases.

Best regards,

Olivier