Emit a failing error code for failing validation.

test/lish/uses_publish_to_url_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.
 
+import 'package:pub/src/exit_codes.dart' as exit_codes;
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
-  integration('preview shows an error if the package is private', () {
+  integration('uses the publish_to URL', () {
     var pkg = packageMap("test_pkg", "1.0.0");
     pkg["publish_to"] = "http://example.com";
     d.dir(appPath, [d.pubspec(pkg)]).create();
 
     schedulePub(args: ["lish", "--dry-run"],
-        output: contains("Publishing test_pkg 1.0.0 to http://example.com"));
+        output: contains("Publishing test_pkg 1.0.0 to http://example.com"),
+        exitCode: exit_codes.DATA);
   });
 }