How to check if a coroutine has finished its execution in the first frame or yield break was called

gistfile1.cs

var coroutineEnumerator = StartCoroutine();
var coroutine = StartCoroutine(coroutineEnumerator);
if(coroutineEnumerator.Current != null)
    yield return coroutine;
else
    //we are here in the same frame if the coroutine ended