Testing shared_preferences on flutter

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');
  });