Barback transforms now pass through the primary input by default.

pkg/barback/test/utils.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.
 
 library barback.test.utils;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert' show Encoding;
 
@@ skipping 231 matching lines @@
 
 Future<LogEntry> _getNextLog(String description) {
   var result = currentSchedule.wrapFuture(
       _barback.log.elementAt(_nextLog++));
   return schedule(() => result, description);
 }
 
 /// Schedules an expectation that the graph will deliver an asset matching
 /// [name] and [contents].
 ///
-/// If [contents] is omitted, defaults to the asset's filename without an
-/// extension (which is the same default that [initGraph] uses).
-void expectAsset(String name, [String contents]) {
+/// [contents] may be a [String] or a [Matcher] that matches a string. If
+/// [contents] is omitted, defaults to the asset's filename without an extension
+/// (which is the same default that [initGraph] uses).
+void expectAsset(String name, [contents]) {
   var id = new AssetId.parse(name);
 
   if (contents == null) {
     contents = pathos.basenameWithoutExtension(id.path);
   }
 
   schedule(() {
     return _barback.getAssetById(id).then((asset) {
       // TODO(rnystrom): Make an actual Matcher class for this.
       expect(asset.id, equals(id));
-      expect(asset.readAsString(), completion(equals(contents)));
+      expect(asset.readAsString(), completion(contents));
     });
   }, "get asset $name");
 }
 
 /// Schedules an expectation that the graph will not find an asset matching
 /// [name].
 void expectNoAsset(String name) {
   var id = new AssetId.parse(name);
 
   // Make sure the future gets the error.
@@ skipping 288 matching lines @@
 
   _MockAsset(this.id, this.contents);
 
   Future<String> readAsString({Encoding encoding}) =>
       new Future.value(contents);
 
   Stream<List<int>> read() => throw new UnimplementedError();
 
   String toString() => "MockAsset $id $contents";
 }