Add sinks to provide synchronous access to events.

test/byte_accumulator_sink_test.dart

+// Copyright (c) 2016, 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:convert/convert.dart';
+import 'package:test/test.dart';
+
+void main() {
+  var sink;
+  setUp(() {
+    sink = new ByteAccumulatorSink();
+  });
+
+  test("provides access to the concatenated bytes", () {
+    expect(sink.bytes, isEmpty);
+
+    sink.add([1, 2, 3]);
+    expect(sink.bytes, equals([1, 2, 3]));
+
+    sink.addSlice([4, 5, 6, 7, 8], 1, 4, false);
+    expect(sink.bytes, equals([1, 2, 3, 5, 6, 7]));
+  });
+
+  test("indicates whether the sink is closed", () {
+    expect(sink.isClosed, isFalse);
+    sink.close();
+    expect(sink.isClosed, isTrue);
+  });
+
+  test("indicates whether the sink is closed via addSlice", () {
+    expect(sink.isClosed, isFalse);
+    sink.addSlice([], 0, 0, true);
+    expect(sink.isClosed, isTrue);
+  });
+
+  test("doesn't allow add() to be called after close()", () {
+    sink.close();
+    expect(() => sink.add([1]), throwsStateError);
+  });
+
+  test("doesn't allow addSlice() to be called after close()", () {
+    sink.close();
+    expect(() => sink.addSlice([], 0, 0, false), throwsStateError);
+  });
+}