fake_async_zone_example.dart

import 'package:flutter_test/flutter_test.dart';

void main() {
  Future<int> outerF;
  final Duration delay = Duration(seconds: 20);

  group('Async Tests - Fake Async', () {
    setUpAll(() async {
      outerF = Future<int>.delayed(delay, () => 42);
      final Stopwatch waiting = Stopwatch()..start();
      final Future<void> innerF = Future<int>.delayed(Duration(seconds: 3), () {});
      await innerF;
      waiting.stop();
      print('Waited for ${waiting.elapsed}');
    });
    // Each testWidgets callback is run in a distinct FakeAsync zone
    testWidgets('Delayed in test, no time added', (WidgetTester tester) async {
      // This will fail due to blowing past the 2 second test case timeout.
      final Future<int> f = Future<int>.delayed(delay, () => 1);
      await f;
    });
    testWidgets('Delayed in test, time added', (WidgetTester tester) async {
      final Future<int> f = Future<int>.delayed(delay, () => 1);
      // So we extend the "time" allowed in the zone, and now it passes.
      // Note that this still runs almost immediately.
      tester.pump(delay);
      await f;
    });
    testWidgets('Delayed from setUp, no time added', (WidgetTester tester) async {
      // This will fail, and will appear to be from a timeout.
      await outerF;
    });
    testWidgets('Delayed from setUp, time added', (WidgetTester tester) async {
      // Even with the "time" added though, it will fail. It will not resolve the
      // future from a different, Real Async, Zone. The error will still look like
      // an exception related to a timeout.
      // It will also run very slow, at least as long as the amount of "time" the
      // tester binding thinks it will take.
      tester.binding.addTime(delay);
      await outerF;
    });
  });
}