Add built-in timeouts to scheduled_test.

pkg/scheduled_test/lib/src/mock_clock.dart

+// Copyright (c) 2013, 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.
+
+/// A library that wraps [Timer] in a way that can be mocked out in test code.
+/// Application code only needs to use [newTimer] to get an instance of [Timer].
+/// Then test code can call [mock] to mock out all new [Timer] instances so that
+/// they're controllable by a returned [Clock] object.
+library mock_clock;
+
+import 'dart:async';
+
+import 'utils.dart';
+
+/// The mock clock object. New [Timer]s will be mocked if and only if this is
+/// non-`null`.
+Clock _clock;
+
+/// Whether or not mocking is active.
+bool get _mocked => _clock != null;
+
+/// Causes all future calls to [newTimer] to return mock [Timer] objects that
+/// are controlled by the returned [Clock]. This may only be called once.
+Clock mock() {
+  if (_mocked) {
+    throw new StateError("mock_clock.mock() has already been called.");
+  }
+
+  _clock = new Clock._();
+  return _clock;
+}
+
+typedef void TimerCallback(Timer timer);
+
+/// Returns a new (possibly mocked) [Timer]. Works the same as [new Timer].
+Timer newTimer(Duration duration, TimerCallback callback) =>
+  _mocked ? new _MockTimer(duration, callback) : new Timer(duration, callback);
+
+/// A clock that controls when mocked [Timer]s move forward in time. It starts
+/// at time 0 and advances forward millisecond-by-millisecond, broadcasting each
+/// tick on the [onTick] stream.
+class Clock {
+  /// The current time of the clock, in milliseconds. Starts at 0.
+  int get time => _time;
+  int _time = 0;
+
+  /// The stream of millisecond ticks of the clock.
+  Stream<int> get onTick => _onTickController.stream;
+  final _onTickController = new StreamController<int>.broadcast();
+
+  Clock._();
+
+  /// Advances the clock forward by [milliseconds]. This works like synchronous
+  /// code that takes [milliseconds] to execute; any [Timer]s that are scheduled
+  /// to fire during the interval will do so asynchronously once control returns
+  /// to the event loop.
+  void tick([int milliseconds=1]) {
+    for (var i = 0; i < milliseconds; i++) {
+      var tickTime = ++_time;
+      new Future.immediate(null).then((_) => _onTickController.add(tickTime));
+    }
+  }
+
+  /// Automatically progresses forward in time as long as there are still
+  /// subscribers to [onTick] (that is, [Timer]s waiting to fire). After each
+  /// tick, this pumps the event loop repeatedly so that all non-clock-dependent
+  /// code runs before the next tick.
+  void run() {
+    pumpEventQueue().then((_) {
+      if (!_onTickController.hasSubscribers) return;
+      tick();
+      return run();
+    });
+  }
+}
+
+/// A mock implementation of [Timer] that uses [Clock] to keep time, rather than
+/// the system clock.
+class _MockTimer implements Timer {
+  /// The time at which the timer should fire.
+  final int _time;
+
+  /// The callback to run when the timer fires.
+  final TimerCallback _callback;
+
+  /// The subscription to the [Clock.onTick] stream.
+  StreamSubscription _subscription;
+
+  // TODO(nweiz): Remove this when issue 8512 is fixed.
+  var _cancelled = false;
+
+  _MockTimer(Duration duration, this._callback)
+      : _time = _clock.time + duration.inMilliseconds {
+    _subscription = _clock.onTick.listen((time) {
+      if (_cancelled || time < _time) return;
+      _subscription.cancel();
+      _callback(this);
+    });
+  }
+
+  void cancel() {
+    _cancelled = true;
+    _subscription.cancel();
+  }
+}