implementation issue from Gary:

¡ñ It is not clear what states constitute 'completed'
¡ñ The test implies 'successfully-completed' and 'unsuccessfullycompleted'
¡ñ However, what happens if a sub-choreography completes with no
finalizers, it automatically transitions to the 'closed' state ¨C which
would currently not be detected by this function
¡ñ Suggestion: change function description to explicitly list states,
and include 'closed' state