| // Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file |
| // for details. All rights reserved. Use of this source code is governed by a |
| // BSD-style license that can be found in the LICENSE file. |
| |
| // @dart = 2.9 |
| |
| import 'dart:async'; |
| import "package:expect/expect.dart"; |
| import "package:async_helper/async_helper.dart"; |
| |
| void main() async { |
| asyncStart(); |
| |
| { |
| // There is a first element. |
| var stream = Stream<int>.value(42); |
| var first = await stream.first; |
| Expect.equals(42, first); |
| // Is single-subscription. |
| Expect.throws(() => stream.first); |
| } |
| |
| { |
| // There is no second element. |
| var stream = Stream<int>.value(42); |
| try { |
| await stream.skip(1).first; |
| Expect.fail("didn't throw"); |
| } on Error { |
| // Success. |
| } |
| } |
| |
| { |
| // There is still no second element. |
| var stream = Stream<int>.value(42); |
| try { |
| await stream.elementAt(1); |
| Expect.fail("didn't throw"); |
| } on Error { |
| // Success. |
| } |
| } |
| |
| { |
| // Works with await for. |
| var stream = Stream<int>.value(42); |
| var value = null; |
| await for (value in stream) {} |
| Expect.equals(42, value); |
| } |
| |
| { |
| // Works with subscriptions and pause-resume. |
| var stream = Stream<int>.value(42); |
| var value; |
| var onDone = Completer(); |
| var sub = stream.listen((v) { |
| value = v; |
| }, onDone: () { |
| Expect.equals(42, value); |
| onDone.complete(); |
| }); |
| sub.pause(); |
| await Future.delayed(Duration(milliseconds: 10)); |
| Expect.isNull(value); |
| Expect.isFalse(onDone.isCompleted); |
| sub.resume(); |
| await onDone.future; |
| } |
| |
| asyncEnd(); |
| } |