Add a ResetTimer class.

test/restartable_timer_test.dart

+// Copyright (c) 2015, 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.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+import 'package:fake_async/fake_async.dart';
+import 'package:test/test.dart';
+
+main() {
+  test("runs the callback once the duration has elapsed", () {
+    new FakeAsync().run((async) {
+      var fired = false;
+      var timer = new RestartableTimer(new Duration(seconds: 5), () {
+        fired = true;
+      });
+
+      async.elapse(new Duration(seconds: 4));
+      expect(fired, isFalse);
+
+      async.elapse(new Duration(seconds: 1));
+      expect(fired, isTrue);
+    });
+  });
+
+  test("doesn't run the callback if the timer is canceled", () {
+    new FakeAsync().run((async) {
+      var fired = false;
+      var timer = new RestartableTimer(new Duration(seconds: 5), () {
+        fired = true;
+      });
+
+      async.elapse(new Duration(seconds: 4));
+      expect(fired, isFalse);
+      timer.cancel();
+
+      async.elapse(new Duration(seconds: 4));
+      expect(fired, isFalse);
+    });
+  });
+
+  test("resets the duration if the timer is reset before it fires", () {
+    new FakeAsync().run((async) {
+      var fired = false;
+      var timer = new RestartableTimer(new Duration(seconds: 5), () {
+        fired = true;
+      });
+
+      async.elapse(new Duration(seconds: 4));
+      expect(fired, isFalse);
+      timer.reset();
+
+      async.elapse(new Duration(seconds: 4));
+      expect(fired, isFalse);
+
+      async.elapse(new Duration(seconds: 1));
+      expect(fired, isTrue);
+    });
+  });
+
+  test("re-runs the callback if the timer is reset after firing", () {
+    new FakeAsync().run((async) {
+      var fired = 0;
+      var timer = new RestartableTimer(new Duration(seconds: 5), () {
+        fired++;
+      });
+
+      async.elapse(new Duration(seconds: 5));
+      expect(fired, equals(1));
+      timer.reset();
+
+      async.elapse(new Duration(seconds: 5));
+      expect(fired, equals(2));
+      timer.reset();
+
+      async.elapse(new Duration(seconds: 5));
+      expect(fired, equals(3));
+    });
+  });
+
+  test("runs the callback if the timer is reset after being canceled", () {
+    new FakeAsync().run((async) {
+      var fired = false;
+      var timer = new RestartableTimer(new Duration(seconds: 5), () {
+        fired = true;
+      });
+
+      async.elapse(new Duration(seconds: 4));
+      expect(fired, isFalse);
+      timer.cancel();
+
+      async.elapse(new Duration(seconds: 4));
+      expect(fired, isFalse);
+      timer.reset();
+
+      async.elapse(new Duration(seconds: 5));
+      expect(fired, isTrue);
+    });
+  });
+
+  test("only runs the callback once if the timer isn't reset", () {
+    new FakeAsync().run((async) {
+      var timer = new RestartableTimer(
+          new Duration(seconds: 5),
+          expectAsync(() {}, count: 1));
+      async.elapse(new Duration(seconds: 10));
+    });
+  });
+}