Use "package:" imports for pub.

test/barback/fails_if_no_default_dirs_test.dart

 // Copyright (c) 2014, 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.
 
+import 'package:pub/src/exit_codes.dart' as exit_codes;
 import 'package:scheduled_test/scheduled_test.dart';
 
-import '../../lib/src/exit_codes.dart' as exit_codes;
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
 
 main() {
   initConfig();
 
   setUp(() {
     d.appDir().create();
   });
 
   pubBuildAndServeShouldFail("if no directories were passed and no default "
           "ones exist",
       args: [],
       buildError: 'Your package must have a "web" directory,\n'
           'or you must specify the source directories.',
       serveError: 'Your package must have "web" and/or "test" directories,\n'
           'or you must specify the source directories.',
       exitCode: exit_codes.DATA);
 }