'test' ['n'|'e'|'p'|'l'|'c'|'s'|'b'|'S'|'L'|
          'se'|'sh' <entity>] |
          ['o' <set>|<node>]
Usually tests the existence of a given entity. And it tests the observability 'o' of a certain node under the given orientation of the model. The node can be given as a member of a set or directly by its node-nr. The command returns TRUE or FALSE and writes it to the ”stack”.