Testing shared_preferences on flutter - testing

Question

I'm writing a flutter application and I'm having this issue when writing the tests. This method is supposed to write data into TextFields and tap a button which saves this data in SharedPrefs:
testWidgets('Click on login saves the credentials',
(WidgetTester tester) async {
await tester.pumpWidget(MyApp());
await tester.enterText(find.byKey(Key('phoneInput')), 'test');
await tester.enterText(find.byKey(Key('passwordInput')), 'test');
await tester.tap(find.byIcon(Icons.lock));
SharedPreferences prefs = await SharedPreferences.getInstance();
expect(prefs.getString('phone'), 'test');
expect(prefs.getString('password'), 'test');
});
This test will fail getting the SharedPreferences instance with this error:
The following TimeoutException was thrown running a test:
TimeoutException after 0:00:03.500000: The test exceeded the timeout. It may have hung.
Consider using "addTime" to increase the timeout before expensive operations.
Update: Seems that the problem is not actually the timeout because even with 60 seconds the test is not capable of resolving the SharedPreferences instance.

Answer 1

You needed to mock getAll from shared_preferences (ref: https://pub.dartlang.org/packages/shared_preferences)
Here's the sample code:
import 'package:shared_preferences/shared_preferences.dart';
import 'package:flutter/services.dart'; // <-- needed for `MethodChannel`
void main() {
setUpAll(() {
const MethodChannel('plugins.flutter.io/shared_preferences')
.setMockMethodCallHandler((MethodCall methodCall) async {
if (methodCall.method == 'getAll') {
return <String, dynamic>{}; // set initial values here if desired
}
return null;
});
});
testWidgets('Click on login saves the credentials',
(WidgetTester tester) async {
await tester.pumpWidget(MyApp());
await tester.enterText(find.byKey(Key('phoneInput')), 'test');
await tester.enterText(find.byKey(Key('passwordInput')), 'test');
await tester.tap(find.byIcon(Icons.lock));
SharedPreferences prefs = await SharedPreferences.getInstance();
expect(prefs.getString('phone'), 'test');
expect(prefs.getString('password'), 'test');
});
}
Original answer:
testWidgets('Click on login saves the credentials',
(WidgetTester tester) async {
final AutomatedTestWidgetsFlutterBinding binding = tester.binding;
binding.addTime(const Duration(seconds: 10)); // or longer if needed
await tester.pumpWidget(MyApp());
await tester.enterText(find.byKey(Key('phoneInput')), 'test');
await tester.enterText(find.byKey(Key('passwordInput')), 'test');
await tester.tap(find.byIcon(Icons.lock));
SharedPreferences prefs = await SharedPreferences.getInstance();
expect(prefs.getString('phone'), 'test');
expect(prefs.getString('password'), 'test');
});

Answer 2

You could use the provided mock setMockInitialValues
testWidgets('Click on login saves the credentials',
(WidgetTester tester) async {
await tester.pumpWidget(MyApp());
SharedPreferences.setMockInitialValues(<String, dynamic>{
'flutter.phone': '',
'flutter.password': '',
});
await tester.enterText(find.byKey(Key('phoneInput')), 'test');
await tester.enterText(find.byKey(Key('passwordInput')), 'test');
await tester.tap(find.byIcon(Icons.lock));
SharedPreferences prefs = await SharedPreferences.getInstance();
expect(prefs.getString('phone'), 'test');
expect(prefs.getString('password'), 'test');
});

Answer 3

As mentioned at github you can do something like this at the beginning of your test:
tester.addTime(const Duration(seconds: 10));
Here is the link and full example :
https://github.com/flutter/flutter/issues/19175
testWidgets('MyWidget', (WidgetTester tester) async {
final AutomatedTestWidgetsFlutterBinding binding = tester.binding;
binding.addTime(const Duration(seconds: 10)); // or longer if needed
await tester.pumpWidget(new MyWidget());
await tester.tap(find.text('Save'));
expect(find.text('Success'), findsOneWidget);
});

Answer 4

The solution provided by TruongSinh was not working for me. When I was trying to set values to SharedPreferences from the code, not tests, I was getting errors.
So here is an addition to that answer. You need to reimplement setters by yourself:
import 'package:flutter/services.dart';
void main() {
setUpAll(() {
final values = <String, dynamic>{}; // set initial values here if desired
const MethodChannel('plugins.flutter.io/shared_preferences')
.setMockMethodCallHandler((MethodCall methodCall) async {
if (methodCall.method == 'getAll') {
return values;
} else if (methodCall.method.startsWith("set")) {
values[methodCall.arguments["key"]] = methodCall.arguments["value"];
return true;
}
return null;
});
});
testWidgets('Test if your code works as designed', (WidgetTester tester) async {
...
});
}