pumpEventQueue function
Returns a Future that completes after the event loop has run the given
number of times (20 by default).
Awaiting this approximates waiting until all asynchronous work (other than work that's waiting for external resources) completes.
Implementation
Future pumpEventQueue({int times}) {
times ??= 20;
if (times == 0) return Future.value();
// Use [new Future] future to allow microtask events to finish. The [new
// Future.value] constructor uses scheduleMicrotask itself and would therefore
// not wait for microtask callbacks that are scheduled after invoking this
// method.
return Future(() => pumpEventQueue(times: times - 1));
}