Make sure that the test follows the naming convention where it makes sense. In this case I would call it:

addEntryListener_whenSameListenerAddedMultipleTimes

And what should the behavior be? I don't know based on the documentation. Perhaps an exception, perhaps the ID returned should be the same. Perhaps different id's. Especially the id part needs to be looked at closer.

As part of your test, you will discover that API's are nto always clear about corner cases. You should push for API changes so that they reflect reality, or you should push for the API to behave like expected. In this case, the API is unclear.