How to write a test for a stateful widget?

Question

I have a stateful widget whose state depends on a async firebase database read call. While the data is being fetched, I display a waiting circular indicator. Once, data fetch is finished, I display the actual ListView widget.

I want to write a widget test to test this functionality. How do i set the value of isReadComplete = true in my test? Or How can I explicitly call success_callback() from my test?

bool isReadComplete;

App(){
   isReadComplete = false;

   firestore.collection('collection').document('doc').get().then((doc) {
      success_callback(doc.data);
    }).catchError((error) => {});
}


void success_callback(var data){
   setState((){
      isReadComplete = true;
   })
}

@override
  Widget build(BuildContext context) {
    if (!isReadComplete) {
      return new CircularIndicator();
    } else {
      List<Widget> widgetList = [];      
      return Scaffold(
          body: ListView(
        padding: EdgeInsets.all(8.0),
        children: widgetList,
      ));
    }
  }

// Test for CircularProgressIndicator

testWidgets("Check CircularProgressIndicator", (WidgetTester tester) async {

      await tester.pumpWidget(new MaterialApp(home: App));

      // This works fine since isReadComplete = false
      expect(find.byType(CircularProgressIndicator), findsOneWidget);
    });

// Test for ListView

testWidgets("Check ListView", (WidgetTester tester) async {

      await tester.pumpWidget(new MaterialApp(home: App));

      // How do I do this? 
      // How to call success_callback()?
      // How to set isReadComplete = true?
      expect(find.byType(ListView), findsOneWidget);
    });

Answer 1

After pumpWidget() , you'd need to call pump() with a Duration set to listen if the Future finishes within the set amount of time. An alternative to pump() is pumpAndSettle() - which calls pump at least once and may repeatedly call pump within a given duration.

await tester.pumpWidget(new MaterialApp(home: App));
await tester.pumpAndSettle();