Flutter: how to test addPostFrameCallback

I have this chunk of code that I would like to test:

if (state is abortView) {
  WidgetsBinding.instance
      .addPostFrameCallback((_) => Navigator.pop(context));
  return Container(key: Key("ContainerToPop"),);
}

In my test I just call the view and expect that should not find anything with that key:

await tester.pumpWidget(_helper.generateApp(state: abortView));
await tester.pump();
expect(find.byKey(Key("ContainerToPop")), findsNothing);

But seems that it doesn't wait for the addPostFrameCallback, it will just evaluate the test in the moment that the container is returned and, of course, will fail.