This reads from asyncIterableP updating iterationObserver with each
successive value. The iterationObserver may only be interested in certain
occurrences (updateState, finish, fail), so for convenience,
observeIteration feature tests for those methods before calling them.
This reads from
asyncIterablePupdatingiterationObserverwith each successive value. TheiterationObservermay only be interested in certain occurrences (updateState,finish,fail), so for convenience,observeIterationfeature tests for those methods before calling them.