This is a wrapper around package:async_helper from the Dart SDK source repo
at //pkg/async_helper that works in the environment of flutter_tester.
This wrapper is needed to ensure that all tests run to completion before the
process exits. This is accomplished by opening a ReceivePort for each test,
which is only closed when the test finishes running.
This package is intended only for use in the flutter/engine repo by unit
tests that run on flutter_tester. Even though the API resembles the API
provided by package:test, it has all the same limitations that
package:async_helper has.