Add the ability to dynamically modify transforms to barback.

pkg/barback/test/package_graph/transform_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.transform_test;
 
 import 'package:barback/src/utils.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../utils.dart';
@@ skipping 1037 matching lines @@
       expectAsset("pkg1|b", "spread out");
       expectAsset("pkg1|c.done", "spread out.done");
       buildShouldSucceed();
 
       modifyAsset("pkg2|a.inc", "b");
       updateSources(["pkg2|a.inc"]);
       expectAsset("pkg1|b", "spread out");
       expectNoAsset("pkg1|c.done");
       buildShouldSucceed();
     });
+
+    test("sees a transformer that's newly applied to a cross-package "
+        "dependency", () {
+      initGraph({
+        "pkg1|a.txt": "pkg2|a.inc",
+        "pkg2|a.inc": "a"
+      }, {
+        "pkg1": [[new ManyToOneTransformer("txt")]],
+        "pkg2": [[new CheckContentTransformer("b", " transformed")]]
+      });
+
+      updateSources(["pkg1|a.txt", "pkg2|a.inc"]);
+      expectAsset("pkg1|a.out", "a");
+      buildShouldSucceed();
+
+      modifyAsset("pkg2|a.inc", "b");
+      updateSources(["pkg2|a.inc"]);
+      expectAsset("pkg1|a.out", "b transformed");
+      buildShouldSucceed();
+    });
+
+    test("doesn't see a transformer that's newly not applied to a "
+        "cross-package dependency", () {
+      initGraph({
+        "pkg1|a.txt": "pkg2|a.inc",
+        "pkg2|a.inc": "a"
+      }, {
+        "pkg1": [[new ManyToOneTransformer("txt")]],
+        "pkg2": [[new CheckContentTransformer("a", " transformed")]]
+      });
+
+      updateSources(["pkg1|a.txt", "pkg2|a.inc"]);
+      expectAsset("pkg1|a.out", "a transformed");
+      buildShouldSucceed();
+
+      modifyAsset("pkg2|a.inc", "b");
+      updateSources(["pkg2|a.inc"]);
+      expectAsset("pkg1|a.out", "b");
+      buildShouldSucceed();
+    });
   });
 }