How to test Cupertino Picker in Flutter - dart

Question

I'm writing widget testing the Cupertino Picker for the different values chosen by the use. I can't find any good tutorial. I followed this https://github.com/flutter/flutter/blob/master/packages/flutter/test/cupertino/picker_test.dart but this won't work for my case. In my case when the user chooses the value from the picker the test case should check whether the user chooses the correct value or default value.
Cupertino Picker code :
List<String> ages1 = ["-- select --"];
List<String> ages2 = List<String>.generate(
45, (int index) => (21 + index).toString(),
growable: false);
List<String> ages = [ages1, ages2].expand((f) => f).toList();
picker.dart:
Widget _buildAgePicker(BuildContext context) {
final FixedExtentScrollController scrollController =
FixedExtentScrollController(initialItem: _selectedAgeIndex);
return GestureDetector(
key: Key("Age Picker"),
onTap: () async {
await showCupertinoModalPopup<void>(
context: context,
builder: (BuildContext context) {
return _buildBottomPicker(
CupertinoPicker(
key: Key("Age picker"),
scrollController: scrollController,
itemExtent: dropDownPickerItemHeight,
backgroundColor: Theme.of(context).canvasColor,
onSelectedItemChanged: (int index) {
setState(() {
_selectedAgeIndex = index;
ageValue = ages[index];
if (ageValue == S.of(context).pickerDefaultValue) {
ageDividerColor = Theme.of(context).errorColor;
errorText = S.of(context).pickerErrorMessage;
ageDividerWidth = 1.2;
} else {
ageDividerColor = Colors.black87;
errorText = "";
ageDividerWidth = 0.4;
}
});
},
children: List<Widget>.generate(ages.length, (int index) {
return Center(
child: Text(ages[index]),
);
}),
),
);
},
);
},
child: _buildMenu(
<Widget>[
Text(
S.of(context).Age,
style: TextStyle(fontSize: 17.0),
),
Text(
ages[_selectedAgeIndex],
),
],
),
);
}
Widget _buildMenu(List<Widget> children) {
return Container(
decoration: BoxDecoration(
color: Theme.of(context).canvasColor,
),
height: 44.0,
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 16.0),
child: SafeArea(
top: false,
bottom: false,
child: DefaultTextStyle(
style: const TextStyle(
color: Colors.black,
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: children,
),
),
),
),
);
}
Widget _buildBottomPicker(Widget picker) {
return Container(
height: dropDownPickerSheetHeight,
padding: const EdgeInsets.only(top: 6.0),
color: Theme.of(context).canvasColor,
child: DefaultTextStyle(
style: const TextStyle(
color: Colors.black,
fontSize: 22.0,
),
child: GestureDetector(
key: Key("picker"),
onTap: () {},
child: SafeArea(
top: false,
child: picker,
),
),
),
);
}
test code :
testWidgets("picker test",(WidgetTester tester)async{
await tester.tap(find.byKey(Key("Age Picker")));
await tester.drag(find.byKey(Key("Age Picker")), Offset(0.0,70.0));
await tester.pumpAndSettle();
expect(ages[1], "21");
});

Answer 1

I used a similar example in my golden test. I modified it a little in order to fit your case. However, the most important part is calling both methods inclusive: fling and drag. If you call only one of them it won't work. At least in my case, that was what happened.
testWidgets("cupertino picker test", (WidgetTester tester) async{
// Find the gesture detector that invoke the cupertino picker
final gestureDetectorFinder = find.byKey(Key('Age Picker'));
await tester.tap(gestureDetectorFinder);
await tester.pump();
// Find the default option (the first one)
final ageFinder = find.text('21').last;
expect(ageFinder, findsOneWidget);
// Apply an offset to scroll
const offset = Offset(0, -10000);
// Use both methods: fling and drag
await tester.fling(
ageFinder,
offset,
1000,
warnIfMissed: false,
);
await tester.drag(
ageFinder,
offset,
warnIfMissed: false,
);
});

Answer 2

What errors did you receive? I've tried creating a minimal repro from the CupertinoPicker snippet you've provided and I did encounter some issues in testWidgets().
Some of the issues that I've noticed is that CupertinoPicker has "Age picker" as its key and GestureDetector has "Age Picker" key set. Note that the key is case-sensitive. Since you're going to test CupertinoPicker, the key set on GestureDetector seems to be unnecessary.
Aside from that, no widget was built for the test. I suggest going through the official docs for Flutter testing to get started https://flutter.dev/docs/cookbook/testing/widget/introduction
Here's the repro I've created from the snippets you've provided.
Code for testing widgets
void main(){
var ages = [18, 19, 20, 21, 22, 24, 24, 25];
testWidgets("CupertinoPicker test", (WidgetTester tester) async {
// build the app for the test
// https://flutter.dev/docs/cookbook/testing/widget/introduction#4-build-the-widget-using-the-widgettester
await tester.pumpWidget(MyApp());
// key should match the key set in the widget
await tester.tap(find.byKey(Key("Age Picker")));
await tester.drag(find.byKey(Key("Age Picker")), Offset(0.0, 70.0));
await tester.pumpAndSettle();
expect(ages[3], 21);
});
}
Sample code for the app
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child:
testPicker(),
),
);
}
var _selectedAgeIndex = 0;
var scrollController = FixedExtentScrollController();
var dropDownPickerItemHeight = 50.0;
var ageValue;
var ages = [18, 19, 20, 21, 22, 24, 24, 25];
testPicker(){
return CupertinoPicker(
key: Key("Age Picker"),
scrollController: scrollController,
itemExtent: dropDownPickerItemHeight,
backgroundColor: Theme.of(context).canvasColor,
onSelectedItemChanged: (int index) {
setState(() {
_selectedAgeIndex = index;
ageValue = ages[index];
print('CupertinoPicker age[$index]: ${ages[index]}');
// if (ageValue == S.of(context).pickerDefaultValue) {
// ageDividerColor = Theme.of(context).errorColor;
// errorText = S.of(context).pickerErrorMessage;
// ageDividerWidth = 1.2;
// } else {
// ageDividerColor = Colors.black87;
// errorText = "";
// ageDividerWidth = 0.4;
// }
});
},
children: List<Widget>.generate(ages.length, (int index) {
return Center(
child: Text('${ages[index]}'),
);
}),
);
}
}