Only run [Transformer.isPrimary] once for each asset/transformer pair.

pkg/barback/test/package_graph/transform/pass_through_test.dart

 // Copyright (c) 2014, 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.transform.pass_through_test;
 
 import 'package:barback/src/utils.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../utils.dart';
@@ skipping 234 matching lines @@
     expectAsset("app|foo.out", "bar");
 
     manyToOne.pauseApply();
     updateSources(["app|bar.in"]);
     expectAssetDoesNotComplete("app|foo.txt");
 
     manyToOne.resumeApply();
     expectAsset("app|foo.txt", "bar.in");
     buildShouldSucceed();
   });
-
-  test("doesn't return an overwritten asset until we know it will still "
-      "be overwritten", () {
-    var rewrite = new RewriteTransformer("txt", "txt");
-    initGraph(["app|foo.txt"], {"app": [[rewrite]]});
-
-    updateSources(["app|foo.txt"]);
-    expectAsset("app|foo.txt", "foo.txt");
-    buildShouldSucceed();
-
-    rewrite.pauseIsPrimary("app|foo.txt");
-    updateSources(["app|foo.txt"]);
-    expectAssetDoesNotComplete("app|foo.txt");
-
-    rewrite.resumeIsPrimary("app|foo.txt");
-    expectAsset("app|foo.txt", "foo.txt");
-    buildShouldSucceed();
-  });
 }