Transition barback's infrastructure to an aggregate-based model.

pkg/barback/test/package_graph/transform/concurrency_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.
 
 /// This library contains tests for transformer behavior that relates to actions
 /// happening concurrently or other complex asynchronous timing behavior.
 library barback.test.package_graph.transform.concurrency_test;
 
 import 'package:barback/src/utils.dart';
 import 'package:scheduled_test/scheduled_test.dart';
@@ skipping 487 matching lines @@
     ]});
 
     pauseProvider();
     updateSources(["app|foo.in"]);
     expectAssetDoesNotComplete("app|foo.in");
 
     resumeProvider();
     expectAsset("app|foo.in", "foo");
     buildShouldSucceed();
   });
+
+  test("re-runs if the primary input is invalidated before accessing", () {
+    var transformer1 = new RewriteTransformer("txt", "mid");
+    var transformer2 = new RewriteTransformer("mid", "out");
+
+    initGraph([
+      "app|foo.txt"
+    ], {"app": [
+      [transformer1],
+      [transformer2]
+    ]});
+
+    transformer2.pausePrimaryInput();
+    updateSources(["app|foo.txt"]);
+
+    // Wait long enough to ensure that transformer1 has completed and
+    // transformer2 has started.
+    schedule(pumpEventQueue);
+
+    // Update the source again so that transformer1 invalidates the primary
+    // input of transformer2.
+    transformer1.pauseApply();
+    modifyAsset("app|foo.txt", "new foo");
+    updateSources(["app|foo.txt"]);
+
+    transformer2.resumePrimaryInput();
+    transformer1.resumeApply();
+
+    expectAsset("app|foo.out", "new foo.mid.out");
+    buildShouldSucceed();
+
+    expect(transformer1.numRuns, completion(equals(2)));
+    expect(transformer2.numRuns, completion(equals(2)));
+  });
 }