Very simple version of Isolates.

sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
 
   // An import error will cause the isolate API to fail synchronously while
   // loading the transformer.
   integration("fails to load a transform with an import error", () {
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
         "transformers": ["myapp/src/transformer"]
       }),
       d.dir("lib", [d.dir("src", [
         d.file("transformer.dart", "import 'does/not/exist.dart';")
       ])])
     ]).create();
 
     createLockFile('myapp', pkg: ['barback']);
-
     var pub = startPub(args: ['serve', '--port=0', "--hostname=127.0.0.1"]);
     expect(pub.nextErrLine(), completion(matches(new RegExp(
         r"Error: line 1 pos 1: library handler failed$"))));
     pub.shouldExit(1);
   });
 }