How to setUp a WidgetTester for Multiple Tests in Flutter

1. The Problem

The testWidgets function is apparently only a subcase of the test function.

A use case I'm trying to solve right now is to pump the same widget for multiple testWidgets, a setUp for multiple testWidgets. However, how can I do this if it creates a new instance inside each test?

I've tried to initialize a WidgetTester outside the tests, in the main(), but WidgetTester has only a private constructor:

class WidgetTester 
  extends WidgetController 
    implements HitTestDispatcher, TickerProvider {
  WidgetTester._(TestWidgetsFlutterBinding binding) : super(binding) {
    if (binding is LiveTestWidgetsFlutterBinding)
      binding.deviceEventDispatcher = this;
}

I don't quite get how the Flutter team made this work, but initializing a WidgetTester in the same way they did inside the testWidgets function isn't working for me:

final TestWidgetsFlutterBinding binding 
  = TestWidgetsFlutterBinding.ensureInitialized() 
    as TestWidgetsFlutterBinding;
final WidgetTester tester = WidgetTester._(binding);

2. An Example

A simple example would be to try to break down the tests of the Flutter demo that is created with each new Flutter project from flutter create. In it, we could try to separate the initial setup test of the app from the tapping action test:

testWidgets('Initial setup', (WidgetTester tester) async {
  await tester.pumpWidget(MyApp());

  expect(find.text('0'), findsOneWidget);
  expect(find.text('1'), findsNothing);
});

testWidgets('Increment the counter on tap', (WidgetTester tester) async {
  await tester.pumpWidget(MyApp());

  await tester.tap(find.byIcon(Icons.add));
  await tester.pump();

  expect(find.text('0'), findsNothing);
  expect(find.text('1'), findsOneWidget);
});

The idea would be to try to move the await tester.pumpWidget(MyApp()); into a setUp function.