| [](https://pub.dev/packages/fake_async) |
| [](https://pub.dev/packages/fake_async/publisher) |
| |
| This package provides a [`FakeAsync`][] class, which makes it easy to |
| deterministically test code that uses asynchronous features like `Future`s, |
| `Stream`s, `Timer`s, and microtasks. It creates an environment in which the user |
| can explicitly control Dart's notion of the "current time". When the time is |
| advanced, `FakeAsync` fires all asynchronous events that are scheduled for that |
| time period without actually needing the test to wait for real time to elapse. |
| |
| [`FakeAsync`]: https://www.dartdocs.org/documentation/fake_async/latest/fake_async/FakeAsync-class.html |
| |
| For example: |
| |
| ```dart |
| import 'dart:async'; |
| |
| import 'package:fake_async/fake_async.dart'; |
| import 'package:test/test.dart'; |
| |
| void main() { |
| test("Future.timeout() throws an error once the timeout is up", () { |
| // Any code run within [fakeAsync] is run within the context of the |
| // [FakeAsync] object passed to the callback. |
| fakeAsync((async) { |
| // All asynchronous features that rely on timing are automatically |
| // controlled by [fakeAsync]. |
| expect(Completer().future.timeout(Duration(seconds: 5)), |
| throwsA(isA<TimeoutException>())); |
| |
| // This will cause the timeout above to fire immediately, without waiting |
| // 5 seconds of real time. |
| async.elapse(Duration(seconds: 5)); |
| }); |
| }); |
| } |
| ``` |
| |
| ## Integration With `clock` |
| |
| `FakeAsync` can't control the time reported by [`DateTime.now()`][] or by |
| the [`Stopwatch`][] class, since they're not part of `dart:async`. However, if |
| you create them using the [`clock`][] package's [`clock.now()`][] or |
| [`clock.stopwatch()`][] functions, `FakeAsync` will automatically override |
| them to use the same notion of time as `dart:async` classes. |
| |
| [`DateTime.now()`]: https://api.dart.dev/stable/dart-core/DateTime/DateTime.now.html |
| [`Stopwatch`]: https://api.dart.dev/stable/dart-core/Stopwatch-class.html |
| [`clock`]: https://pub.dev/packages/clock |
| [`clock.now()`]: https://pub.dev/documentation/clock/latest/clock/Clock/now.html |
| [`clock.stopwatch()`]: https://pub.dev/documentation/clock/latest/clock/Clock/stopwatch.html |
