Add a StreamSinkCompleter class.

test/utils.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.
 
 /// Helper utilities for testing.
 library async.test.util;
 
 import "dart:async";
+
+import "package:async/async.dart";
 import "package:test/test.dart";
 
 /// A zero-millisecond timer should wait until after all microtasks.
 Future flushMicrotasks() => new Future.delayed(Duration.ZERO);
 
 /// A generic unreachable callback function.
 ///
 /// Returns a function that fails the test if it is ever called.
 unreachable(String name) => ([a, b]) => fail("Unreachable: $name");
 
@@ skipping 14 matching lines @@
 class CompleterStreamSink<T> implements StreamSink<T> {
   final completer = new Completer();
 
   Future get done => completer.future;
 
   void add(T event) {}
   void addError(error, [StackTrace stackTrace]) {}
   Future addStream(Stream<T> stream) async {}
   Future close() => completer.future;
 }
+
+/// A [StreamSink] that collects all events added to it as results.
+///
+/// This is used for testing code that interacts with sinks.
+class TestSink<T> implements StreamSink<T> {
+  /// The results corresponding to events that have been added to the sink.
+  final results = <Result<T>>[];
+
+  /// Whether [close] has been called.
+  bool get isClosed => _isClosed;
+  var _isClosed = false;
+
+  Future get done => _doneCompleter.future;
+  final _doneCompleter = new Completer();
+
+  final Function _onDone;
+
+  /// Creates a new sink.
+  ///
+  /// If [onDone] is passed, it's called when the user calls [close]. Its result
+  /// is piped to the [done] future.
+  TestSink({onDone()}) : _onDone = onDone ?? (() {});
+
+  void add(T event) {
+    results.add(new Result<T>.value(event));
+  }
+
+  void addError(error, [StackTrace stackTrace]) {
+    results.add(new Result<T>.error(error, stackTrace));
+  }
+
+  Future addStream(Stream<T> stream) {
+    var completer = new Completer.sync();
+    stream.listen(add, onError: addError, onDone: completer.complete);
+    return completer.future;
+  }
+
+  Future close() {
+    _isClosed = true;
+    _doneCompleter.complete(new Future.microtask(_onDone));
+    return done;
+  }
+}