Async operations don't complete inside testWidgets()

[markstory]

I'm working on my first flutter application, so I may have missed an obvious solution to this. I'm running into problems interacting with json_cache + localstorage within the context of tests. I've attempted to create a minimal reprodction.

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

import 'package:json_cache/json_cache.dart';
import 'package:localstorage/localstorage.dart';

void main() {
  TestWidgetsFlutterBinding.ensureInitialized();

  testWidgets('database insert', (tester) async {
    final LocalStorage storage = LocalStorage('test-idea');
    var database = JsonCacheMem(JsonCacheLocalStorage(storage));
    print('before');
    await database.refresh('test', {'k': 'v'});
    print('set value');
  });
}

When I run this test with flutter test it prints before but never prints set value. However, if I use test() instead of testWidgets() the test completes successfully. The broader context of what I'm trying to do is, write a more complex test case where I display a form. That form contains dropdown menus that contain data that would be read from json_cache, but I'm not currently able to get data into json_cache.

[markstory]

I did some more poking around and found that storing data into json_cache works fine if I do it in setUp(). Is it best to avoid writing data inside testWidgets()?

[rafamizes]

First of all, thanks for opening this issue.

I will try to reproduce the problem you reported on my machine and let you know as soon as I have some results.

[rafamizes]

Hello.

It seems to be a problem with the Localstore package, as someone else reported a similar error: Localstorage ready not gets called when using flutter_test.

I will still do further analysis to gather more information.

[markstory]

First of all, thanks for opening this issue.

You're welcome ❤️ Thank you for putting this library together, I've been loving it so far.

[rafamizes]

Hi again.

It all boils down to a race condition with the testWidgets method that is causing a deadlock inside Localstorage. All you need to do to fix this is to run your test code inside a tester.runAsync method.

For your particular case, the unit test code should look like this:

testWidgets('database insert', (WidgetTester tester) async {
  final LocalStorage storage = LocalStorage('test-idea');
  final database = JsonCacheMem(JsonCacheLocalStorage(storage));
  tester.runAsync(() async {
    print('before');
    await database.refresh('test', <String, dynamic>{'k': 'v'});
    print('set value');
  });
});

Please let me know if the previous tip worked so that I can close this issue.

Regards.

[markstory]

@rafamizes Yes, using runAsync() to update localstorage works perfectly. Thank you so much.

[rafamizes]

@markstory You're welcome.

Whenever you need help or have a suggestion to improve this package, feel free to open an issue. I will try to fix/improve it as soon as I can.

By the way, if you are programming code related to forms (which is sometimes a nuisance in Flutter), the following package might be useful for you well_formed. As usual, new features can be added on demand — all you have to do is open new issues to request them.

Cheers!