Fine tune model - choosing test completion from a closed list not in the training set

hello all,
I trained a fine tune model (ada) for few payers with a closed list of completions.
can I test it on different payers not from the list and ask openAI to choose a GL expense accounts from a closed list that not related to the trained data?
similar groups but different names. my purpose that he will learn from the content of the train to the test but choose a different name from a closed list. I tried so far few option in the test prompt but nothing seem to work so far.