First stab at "pub run" command.

sdk/lib/_internal/pub/test/run/runs_a_generated_script_test.dart

Index: sdk/lib/_internal/pub/test/run/runs_a_generated_script_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/supports_a_transformer_that_doesnt_return_futures_test.dart b/sdk/lib/_internal/pub/test/run/runs_a_generated_script_test.dart
similarity index 52%
copy from sdk/lib/_internal/pub/test/transformer/supports_a_transformer_that_doesnt_return_futures_test.dart
copy to sdk/lib/_internal/pub/test/run/runs_a_generated_script_test.dart
index 0d67187c9c019d8f6dcec3e920f1e3c5d6c68ed3..daedf2567873e462f16c90f5f8020a0ae9cb2585 100644
--- a/sdk/lib/_internal/pub/test/transformer/supports_a_transformer_that_doesnt_return_futures_test.dart
+++ b/sdk/lib/_internal/pub/test/run/runs_a_generated_script_test.dart
@@ -1,30 +1,25 @@
-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS d.file
+// 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 pub_tests;
-
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
-import '../serve/utils.dart';
+import 'utils.dart';
 
 const TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
-class RewriteTransformer extends Transformer implements DeclaringTransformer {
-  RewriteTransformer.asPlugin();
+class DartTransformer extends Transformer {
+  DartTransformer.asPlugin();
 
-  bool isPrimary(AssetId id) => id.extension == '.txt';
+  String get allowedExtensions => '.in';
 
   void apply(Transform transform) {
     transform.addOutput(new Asset.fromString(
-        transform.primaryInput.id, "new contents"));
-  }
-
-  void declareOutputs(DeclaringTransform transform) {
-    transform.declareOutput(transform.primaryId);
+        new AssetId("myapp", "bin/script.dart"),
+        "void main() => print('generated');"));
   }
 }
 """;
@@ -32,25 +27,25 @@ class RewriteTransformer extends Transformer implements DeclaringTransformer {
 main() {
   initConfig();
   withBarbackVersions("any", () {
-    integration("supports a transformer that doesn't return futures", () {
+    integration('runs a script generated from scratch by a transformer', () {
       d.dir(appPath, [
         d.pubspec({
           "name": "myapp",
           "transformers": ["myapp/src/transformer"]
         }),
         d.dir("lib", [d.dir("src", [
-          d.file("transformer.dart", TRANSFORMER)
-        ])]),
-        d.dir("web", [
-          d.file("foo.txt", "foo")
-        ])
+          d.file("transformer.dart", TRANSFORMER),
+          d.file("primary.in", "")
+        ])])
       ]).create();
 
       createLockFile('myapp', pkg: ['barback']);
 
-      pubServe();
-      requestShouldSucceed("foo.txt", "new contents");
-      endPubServe();
+      var pub = pubRun(args: ["script"],
+          transformers: ["myapp/src/transformer"]);
+
+      pub.stdout.expect("generated");
+      pub.shouldExit();
     });
   });
 }