Move Barback to a more thoroughly push-based model.

pkg/barback/test/package_graph/errors_test.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.package_graph.source_test;
 
 import 'package:barback/src/utils.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../utils.dart';
@@ skipping 250 matching lines @@
     }, {"app": [[rewrite1, rewrite2, rewrite3]]});
 
     // Make rewrite3 the most-recently-completed transformer from the first run.
     rewrite2.pauseApply();
     rewrite3.pauseApply();
     updateSources(["app|foo.one", "app|foo.two", "app|foo.three"]);
     schedule(pumpEventQueue);
     rewrite2.resumeApply();
     schedule(pumpEventQueue);
     rewrite3.resumeApply();
-    buildShouldFail([isAssetCollisionException("app|foo.out")]);
+    buildShouldFail([
+      isAssetCollisionException("app|foo.out"),
+      isAssetCollisionException("app|foo.out")
+    ]);
 
     // Then update rewrite3 in a separate build. rewrite2 should still be the
     // next version of foo.out in line.
     // TODO(nweiz): Should this emit a collision error as well? Or should they
     // only be emitted when a file is added or removed?
     updateSources(["app|foo.three"]);
     buildShouldSucceed();
 
     removeSources(["app|foo.one"]);
     expectAsset("app|foo.out", "two.out");
@@ skipping 42 matching lines @@
 
     updateSources(["app|foo.txt"]);
     expectAsset("app|foo.txt", "foo");
     buildShouldSucceed();
 
     updateSources(["app|foo.in"]);
     expectAsset("app|foo.txt", "foo");
     buildShouldFail([isAssetCollisionException("app|foo.txt")]);
   });
 }