Out of ads and triggering other error messages.

I was looking around, but couldn't find these details and was hoping someone here could clarify. I have two somewhat related questions:

1. What happens when there are no ads available? Does the listener go to a regular error state (
   UnityAds.FinishState.ERROR)?
2. Is there a way to trigger an error state during testing? I tried turning off internet connectivity, but still wasn't able to trigger the onUnityAdsErrormessage, or reach the UnityAds.FinishState.ERROR state.

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Out of ads and triggering other error messages.