Add an AssetStream class to Barback.

pkg/barback/test/stream_replayer_test.dart

Index: pkg/barback/test/stream_replayer_test.dart
diff --git a/pkg/barback/test/stream_replayer_test.dart b/pkg/barback/test/stream_replayer_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..49f60bad5c3352b55f91a6c75b5c0de9277ee4a4
--- /dev/null
+++ b/pkg/barback/test/stream_replayer_test.dart
@@ -0,0 +1,57 @@
+// 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.
+
+library barback.test.stream_replayer_test;
+
+import 'dart:async';
+
+import 'package:barback/src/stream_replayer.dart';
+import 'package:unittest/unittest.dart';
+
+import 'utils.dart';
+
+main() {
+  initConfig();
+
+  test("a replay that's retrieved before the stream is finished replays the "
+      "stream", () {
+    var controller = new StreamController<int>();
+    var replay = new StreamReplayer<int>(controller.stream).getReplay();
+
+    controller.add(1);
+    controller.add(2);
+    controller.add(3);
+    controller.close();
+
+    expect(replay.toList(), completion(equals([1, 2, 3])));
+  });
+
+  test("a replay that's retrieved after the stream is finished replays the "
+      "stream", () {
+    var controller = new StreamController<int>();
+    var replayer = new StreamReplayer<int>(controller.stream);
+
+    controller.add(1);
+    controller.add(2);
+    controller.add(3);
+    controller.close();
+
+    expect(replayer.getReplay().toList(), completion(equals([1, 2, 3])));
+  });
+
+  test("multiple replays each replay the stream", () {
+    var controller = new StreamController<int>();
+    var replayer = new StreamReplayer<int>(controller.stream);
+
+    var replay1 = replayer.getReplay();
+    controller.add(1);
+    controller.add(2);
+    controller.add(3);
+    controller.close();
+    var replay2 = replayer.getReplay();
+
+    expect(replay1.toList(), completion(equals([1, 2, 3])));
+    expect(replay2.toList(), completion(equals([1, 2, 3])));
+  });
+}